Merge tag 'rcu-urgent.2022.12.17a' of git://git.kernel.org/pub/scm/linux/kernel/git...

[mirror_ubuntu-kernels.git] / fs / xattr.c

// SPDX-License-Identifier: GPL-2.0-only
/*
  File: fs/xattr.c

  Extended attribute handling.

  Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
  Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
  Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
 */
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/xattr.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/evm.h>
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/fsnotify.h>
#include <linux/audit.h>
#include <linux/vmalloc.h>
#include <linux/posix_acl_xattr.h>

#include <linux/uaccess.h>

#include "internal.h"

static const char *
strcmp_prefix(const char *a, const char *a_prefix)
{
        while (*a_prefix && *a == *a_prefix) {
                a++;
                a_prefix++;
        }
        return *a_prefix ? NULL : a;
}

/*
 * In order to implement different sets of xattr operations for each xattr
 * prefix, a filesystem should create a null-terminated array of struct
 * xattr_handler (one for each prefix) and hang a pointer to it off of the
 * s_xattr field of the superblock.
 */
#define for_each_xattr_handler(handlers, handler)               \
        if (handlers)                                           \
                for ((handler) = *(handlers)++;                 \
                        (handler) != NULL;                      \
                        (handler) = *(handlers)++)

/*
 * Find the xattr_handler with the matching prefix.
 */
static const struct xattr_handler *
xattr_resolve_name(struct inode *inode, const char **name)
{
        const struct xattr_handler **handlers = inode->i_sb->s_xattr;
        const struct xattr_handler *handler;

        if (!(inode->i_opflags & IOP_XATTR)) {
                if (unlikely(is_bad_inode(inode)))
                        return ERR_PTR(-EIO);
                return ERR_PTR(-EOPNOTSUPP);
        }
        for_each_xattr_handler(handlers, handler) {
                const char *n;

                n = strcmp_prefix(*name, xattr_prefix(handler));
                if (n) {
                        if (!handler->prefix ^ !*n) {
                                if (*n)
                                        continue;
                                return ERR_PTR(-EINVAL);
                        }
                        *name = n;
                        return handler;
                }
        }
        return ERR_PTR(-EOPNOTSUPP);
}

/**
 * may_write_xattr - check whether inode allows writing xattr
 * @mnt_userns: User namespace of the mount the inode was found from
 * @inode: the inode on which to set an xattr
 *
 * Check whether the inode allows writing xattrs. Specifically, we can never
 * set or remove an extended attribute on a read-only filesystem  or on an
 * immutable / append-only inode.
 *
 * We also need to ensure that the inode has a mapping in the mount to
 * not risk writing back invalid i_{g,u}id values.
 *
 * Return: On success zero is returned. On error a negative errno is returned.
 */
int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode)
{
        if (IS_IMMUTABLE(inode))
                return -EPERM;
        if (IS_APPEND(inode))
                return -EPERM;
        if (HAS_UNMAPPED_ID(mnt_userns, inode))
                return -EPERM;
        return 0;
}

/*
 * Check permissions for extended attribute access.  This is a bit complicated
 * because different namespaces have very different rules.
 */
static int
xattr_permission(struct user_namespace *mnt_userns, struct inode *inode,
                 const char *name, int mask)
{
        if (mask & MAY_WRITE) {
                int ret;

                ret = may_write_xattr(mnt_userns, inode);
                if (ret)
                        return ret;
        }

        /*
         * No restriction for security.* and system.* from the VFS.  Decision
         * on these is left to the underlying filesystem / security module.
         */
        if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
            !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
                return 0;

        /*
         * The trusted.* namespace can only be accessed by privileged users.
         */
        if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
                if (!capable(CAP_SYS_ADMIN))
                        return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
                return 0;
        }

        /*
         * In the user.* namespace, only regular files and directories can have
         * extended attributes. For sticky directories, only the owner and
         * privileged users can write attributes.
         */
        if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
                if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
                        return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
                if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
                    (mask & MAY_WRITE) &&
                    !inode_owner_or_capable(mnt_userns, inode))
                        return -EPERM;
        }

        return inode_permission(mnt_userns, inode, mask);
}

/*
 * Look for any handler that deals with the specified namespace.
 */
int
xattr_supported_namespace(struct inode *inode, const char *prefix)
{
        const struct xattr_handler **handlers = inode->i_sb->s_xattr;
        const struct xattr_handler *handler;
        size_t preflen;

        if (!(inode->i_opflags & IOP_XATTR)) {
                if (unlikely(is_bad_inode(inode)))
                        return -EIO;
                return -EOPNOTSUPP;
        }

        preflen = strlen(prefix);

        for_each_xattr_handler(handlers, handler) {
                if (!strncmp(xattr_prefix(handler), prefix, preflen))
                        return 0;
        }

        return -EOPNOTSUPP;
}
EXPORT_SYMBOL(xattr_supported_namespace);

int
__vfs_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
               struct inode *inode, const char *name, const void *value,
               size_t size, int flags)
{
        const struct xattr_handler *handler;

        if (is_posix_acl_xattr(name))
                return -EOPNOTSUPP;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->set)
                return -EOPNOTSUPP;
        if (size == 0)
                value = "";  /* empty EA, do not remove */
        return handler->set(handler, mnt_userns, dentry, inode, name, value,
                            size, flags);
}
EXPORT_SYMBOL(__vfs_setxattr);

/**
 *  __vfs_setxattr_noperm - perform setxattr operation without performing
 *  permission checks.
 *
 *  @mnt_userns: user namespace of the mount the inode was found from
 *  @dentry: object to perform setxattr on
 *  @name: xattr name to set
 *  @value: value to set @name to
 *  @size: size of @value
 *  @flags: flags to pass into filesystem operations
 *
 *  returns the result of the internal setxattr or setsecurity operations.
 *
 *  This function requires the caller to lock the inode's i_mutex before it
 *  is executed. It also assumes that the caller will make the appropriate
 *  permission checks.
 */
int __vfs_setxattr_noperm(struct user_namespace *mnt_userns,
                          struct dentry *dentry, const char *name,
                          const void *value, size_t size, int flags)
{
        struct inode *inode = dentry->d_inode;
        int error = -EAGAIN;
        int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
                                   XATTR_SECURITY_PREFIX_LEN);

        if (issec)
                inode->i_flags &= ~S_NOSEC;
        if (inode->i_opflags & IOP_XATTR) {
                error = __vfs_setxattr(mnt_userns, dentry, inode, name, value,
                                       size, flags);
                if (!error) {
                        fsnotify_xattr(dentry);
                        security_inode_post_setxattr(dentry, name, value,
                                                     size, flags);
                }
        } else {
                if (unlikely(is_bad_inode(inode)))
                        return -EIO;
        }
        if (error == -EAGAIN) {
                error = -EOPNOTSUPP;

                if (issec) {
                        const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;

                        error = security_inode_setsecurity(inode, suffix, value,
                                                           size, flags);
                        if (!error)
                                fsnotify_xattr(dentry);
                }
        }

        return error;
}

/**
 * __vfs_setxattr_locked - set an extended attribute while holding the inode
 * lock
 *
 *  @mnt_userns: user namespace of the mount of the target inode
 *  @dentry: object to perform setxattr on
 *  @name: xattr name to set
 *  @value: value to set @name to
 *  @size: size of @value
 *  @flags: flags to pass into filesystem operations
 *  @delegated_inode: on return, will contain an inode pointer that
 *  a delegation was broken on, NULL if none.
 */
int
__vfs_setxattr_locked(struct user_namespace *mnt_userns, struct dentry *dentry,
                      const char *name, const void *value, size_t size,
                      int flags, struct inode **delegated_inode)
{
        struct inode *inode = dentry->d_inode;
        int error;

        error = xattr_permission(mnt_userns, inode, name, MAY_WRITE);
        if (error)
                return error;

        error = security_inode_setxattr(mnt_userns, dentry, name, value, size,
                                        flags);
        if (error)
                goto out;

        error = try_break_deleg(inode, delegated_inode);
        if (error)
                goto out;

        error = __vfs_setxattr_noperm(mnt_userns, dentry, name, value,
                                      size, flags);

out:
        return error;
}
EXPORT_SYMBOL_GPL(__vfs_setxattr_locked);

int
vfs_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
             const char *name, const void *value, size_t size, int flags)
{
        struct inode *inode = dentry->d_inode;
        struct inode *delegated_inode = NULL;
        const void  *orig_value = value;
        int error;

        if (size && strcmp(name, XATTR_NAME_CAPS) == 0) {
                error = cap_convert_nscap(mnt_userns, dentry, &value, size);
                if (error < 0)
                        return error;
                size = error;
        }

retry_deleg:
        inode_lock(inode);
        error = __vfs_setxattr_locked(mnt_userns, dentry, name, value, size,
                                      flags, &delegated_inode);
        inode_unlock(inode);

        if (delegated_inode) {
                error = break_deleg_wait(&delegated_inode);
                if (!error)
                        goto retry_deleg;
        }
        if (value != orig_value)
                kfree(value);

        return error;
}
EXPORT_SYMBOL_GPL(vfs_setxattr);

static ssize_t
xattr_getsecurity(struct user_namespace *mnt_userns, struct inode *inode,
                  const char *name, void *value, size_t size)
{
        void *buffer = NULL;
        ssize_t len;

        if (!value || !size) {
                len = security_inode_getsecurity(mnt_userns, inode, name,
                                                 &buffer, false);
                goto out_noalloc;
        }

        len = security_inode_getsecurity(mnt_userns, inode, name, &buffer,
                                         true);
        if (len < 0)
                return len;
        if (size < len) {
                len = -ERANGE;
                goto out;
        }
        memcpy(value, buffer, len);
out:
        kfree(buffer);
out_noalloc:
        return len;
}

/*
 * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
 *
 * Allocate memory, if not already allocated, or re-allocate correct size,
 * before retrieving the extended attribute.  The xattr value buffer should
 * always be freed by the caller, even on error.
 *
 * Returns the result of alloc, if failed, or the getxattr operation.
 */
int
vfs_getxattr_alloc(struct user_namespace *mnt_userns, struct dentry *dentry,
                   const char *name, char **xattr_value, size_t xattr_size,
                   gfp_t flags)
{
        const struct xattr_handler *handler;
        struct inode *inode = dentry->d_inode;
        char *value = *xattr_value;
        int error;

        error = xattr_permission(mnt_userns, inode, name, MAY_READ);
        if (error)
                return error;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->get)
                return -EOPNOTSUPP;
        error = handler->get(handler, dentry, inode, name, NULL, 0);
        if (error < 0)
                return error;

        if (!value || (error > xattr_size)) {
                value = krealloc(*xattr_value, error + 1, flags);
                if (!value)
                        return -ENOMEM;
                memset(value, 0, error + 1);
        }

        error = handler->get(handler, dentry, inode, name, value, error);
        *xattr_value = value;
        return error;
}

ssize_t
__vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
               void *value, size_t size)
{
        const struct xattr_handler *handler;

        if (is_posix_acl_xattr(name))
                return -EOPNOTSUPP;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->get)
                return -EOPNOTSUPP;
        return handler->get(handler, dentry, inode, name, value, size);
}
EXPORT_SYMBOL(__vfs_getxattr);

ssize_t
vfs_getxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
             const char *name, void *value, size_t size)
{
        struct inode *inode = dentry->d_inode;
        int error;

        error = xattr_permission(mnt_userns, inode, name, MAY_READ);
        if (error)
                return error;

        error = security_inode_getxattr(dentry, name);
        if (error)
                return error;

        if (!strncmp(name, XATTR_SECURITY_PREFIX,
                                XATTR_SECURITY_PREFIX_LEN)) {
                const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
                int ret = xattr_getsecurity(mnt_userns, inode, suffix, value,
                                            size);
                /*
                 * Only overwrite the return value if a security module
                 * is actually active.
                 */
                if (ret == -EOPNOTSUPP)
                        goto nolsm;
                return ret;
        }
nolsm:
        return __vfs_getxattr(dentry, inode, name, value, size);
}
EXPORT_SYMBOL_GPL(vfs_getxattr);

ssize_t
vfs_listxattr(struct dentry *dentry, char *list, size_t size)
{
        struct inode *inode = d_inode(dentry);
        ssize_t error;

        error = security_inode_listxattr(dentry);
        if (error)
                return error;
        if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
                error = inode->i_op->listxattr(dentry, list, size);
        } else {
                error = security_inode_listsecurity(inode, list, size);
                if (size && error > size)
                        error = -ERANGE;
        }
        return error;
}
EXPORT_SYMBOL_GPL(vfs_listxattr);

int
__vfs_removexattr(struct user_namespace *mnt_userns, struct dentry *dentry,
                  const char *name)
{
        struct inode *inode = d_inode(dentry);
        const struct xattr_handler *handler;

        if (is_posix_acl_xattr(name))
                return -EOPNOTSUPP;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->set)
                return -EOPNOTSUPP;
        return handler->set(handler, mnt_userns, dentry, inode, name, NULL, 0,
                            XATTR_REPLACE);
}
EXPORT_SYMBOL(__vfs_removexattr);

/**
 * __vfs_removexattr_locked - set an extended attribute while holding the inode
 * lock
 *
 *  @mnt_userns: user namespace of the mount of the target inode
 *  @dentry: object to perform setxattr on
 *  @name: name of xattr to remove
 *  @delegated_inode: on return, will contain an inode pointer that
 *  a delegation was broken on, NULL if none.
 */
int
__vfs_removexattr_locked(struct user_namespace *mnt_userns,
                         struct dentry *dentry, const char *name,
                         struct inode **delegated_inode)
{
        struct inode *inode = dentry->d_inode;
        int error;

        error = xattr_permission(mnt_userns, inode, name, MAY_WRITE);
        if (error)
                return error;

        error = security_inode_removexattr(mnt_userns, dentry, name);
        if (error)
                goto out;

        error = try_break_deleg(inode, delegated_inode);
        if (error)
                goto out;

        error = __vfs_removexattr(mnt_userns, dentry, name);

        if (!error) {
                fsnotify_xattr(dentry);
                evm_inode_post_removexattr(dentry, name);
        }

out:
        return error;
}
EXPORT_SYMBOL_GPL(__vfs_removexattr_locked);

int
vfs_removexattr(struct user_namespace *mnt_userns, struct dentry *dentry,
                const char *name)
{
        struct inode *inode = dentry->d_inode;
        struct inode *delegated_inode = NULL;
        int error;

retry_deleg:
        inode_lock(inode);
        error = __vfs_removexattr_locked(mnt_userns, dentry,
                                         name, &delegated_inode);
        inode_unlock(inode);

        if (delegated_inode) {
                error = break_deleg_wait(&delegated_inode);
                if (!error)
                        goto retry_deleg;
        }

        return error;
}
EXPORT_SYMBOL_GPL(vfs_removexattr);

/*
 * Extended attribute SET operations
 */

int setxattr_copy(const char __user *name, struct xattr_ctx *ctx)
{
        int error;

        if (ctx->flags & ~(XATTR_CREATE|XATTR_REPLACE))
                return -EINVAL;

        error = strncpy_from_user(ctx->kname->name, name,
                                sizeof(ctx->kname->name));
        if (error == 0 || error == sizeof(ctx->kname->name))
                return  -ERANGE;
        if (error < 0)
                return error;

        error = 0;
        if (ctx->size) {
                if (ctx->size > XATTR_SIZE_MAX)
                        return -E2BIG;

                ctx->kvalue = vmemdup_user(ctx->cvalue, ctx->size);
                if (IS_ERR(ctx->kvalue)) {
                        error = PTR_ERR(ctx->kvalue);
                        ctx->kvalue = NULL;
                }
        }

        return error;
}

int do_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
                struct xattr_ctx *ctx)
{
        if (is_posix_acl_xattr(ctx->kname->name))
                return do_set_acl(idmap, dentry, ctx->kname->name,
                                  ctx->kvalue, ctx->size);

        return vfs_setxattr(mnt_idmap_owner(idmap), dentry, ctx->kname->name,
                        ctx->kvalue, ctx->size, ctx->flags);
}

static long
setxattr(struct mnt_idmap *idmap, struct dentry *d,
        const char __user *name, const void __user *value, size_t size,
        int flags)
{
        struct xattr_name kname;
        struct xattr_ctx ctx = {
                .cvalue   = value,
                .kvalue   = NULL,
                .size     = size,
                .kname    = &kname,
                .flags    = flags,
        };
        int error;

        error = setxattr_copy(name, &ctx);
        if (error)
                return error;

        error = do_setxattr(idmap, d, &ctx);

        kvfree(ctx.kvalue);
        return error;
}

static int path_setxattr(const char __user *pathname,
                         const char __user *name, const void __user *value,
                         size_t size, int flags, unsigned int lookup_flags)
{
        struct path path;
        int error;

retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = mnt_want_write(path.mnt);
        if (!error) {
                error = setxattr(mnt_idmap(path.mnt), path.dentry, name,
                                 value, size, flags);
                mnt_drop_write(path.mnt);
        }
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
                const char __user *, name, const void __user *, value,
                size_t, size, int, flags)
{
        return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
                const char __user *, name, const void __user *, value,
                size_t, size, int, flags)
{
        return path_setxattr(pathname, name, value, size, flags, 0);
}

SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
                const void __user *,value, size_t, size, int, flags)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = mnt_want_write_file(f.file);
        if (!error) {
                error = setxattr(file_mnt_idmap(f.file),
                                 f.file->f_path.dentry, name,
                                 value, size, flags);
                mnt_drop_write_file(f.file);
        }
        fdput(f);
        return error;
}

/*
 * Extended attribute GET operations
 */
ssize_t
do_getxattr(struct mnt_idmap *idmap, struct dentry *d,
        struct xattr_ctx *ctx)
{
        ssize_t error;
        char *kname = ctx->kname->name;

        if (ctx->size) {
                if (ctx->size > XATTR_SIZE_MAX)
                        ctx->size = XATTR_SIZE_MAX;
                ctx->kvalue = kvzalloc(ctx->size, GFP_KERNEL);
                if (!ctx->kvalue)
                        return -ENOMEM;
        }

        if (is_posix_acl_xattr(ctx->kname->name))
                error = do_get_acl(idmap, d, kname, ctx->kvalue, ctx->size);
        else
                error = vfs_getxattr(mnt_idmap_owner(idmap), d, kname,
                                     ctx->kvalue, ctx->size);
        if (error > 0) {
                if (ctx->size && copy_to_user(ctx->value, ctx->kvalue, error))
                        error = -EFAULT;
        } else if (error == -ERANGE && ctx->size >= XATTR_SIZE_MAX) {
                /* The file system tried to returned a value bigger
                   than XATTR_SIZE_MAX bytes. Not possible. */
                error = -E2BIG;
        }

        return error;
}

static ssize_t
getxattr(struct mnt_idmap *idmap, struct dentry *d,
         const char __user *name, void __user *value, size_t size)
{
        ssize_t error;
        struct xattr_name kname;
        struct xattr_ctx ctx = {
                .value    = value,
                .kvalue   = NULL,
                .size     = size,
                .kname    = &kname,
                .flags    = 0,
        };

        error = strncpy_from_user(kname.name, name, sizeof(kname.name));
        if (error == 0 || error == sizeof(kname.name))
                error = -ERANGE;
        if (error < 0)
                return error;

        error =  do_getxattr(idmap, d, &ctx);

        kvfree(ctx.kvalue);
        return error;
}

static ssize_t path_getxattr(const char __user *pathname,
                             const char __user *name, void __user *value,
                             size_t size, unsigned int lookup_flags)
{
        struct path path;
        ssize_t error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = getxattr(mnt_idmap(path.mnt), path.dentry, name, value, size);
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
                const char __user *, name, void __user *, value, size_t, size)
{
        return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
                const char __user *, name, void __user *, value, size_t, size)
{
        return path_getxattr(pathname, name, value, size, 0);
}

SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
                void __user *, value, size_t, size)
{
        struct fd f = fdget(fd);
        ssize_t error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = getxattr(file_mnt_idmap(f.file), f.file->f_path.dentry,
                         name, value, size);
        fdput(f);
        return error;
}

/*
 * Extended attribute LIST operations
 */
static ssize_t
listxattr(struct dentry *d, char __user *list, size_t size)
{
        ssize_t error;
        char *klist = NULL;

        if (size) {
                if (size > XATTR_LIST_MAX)
                        size = XATTR_LIST_MAX;
                klist = kvmalloc(size, GFP_KERNEL);
                if (!klist)
                        return -ENOMEM;
        }

        error = vfs_listxattr(d, klist, size);
        if (error > 0) {
                if (size && copy_to_user(list, klist, error))
                        error = -EFAULT;
        } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
                /* The file system tried to returned a list bigger
                   than XATTR_LIST_MAX bytes. Not possible. */
                error = -E2BIG;
        }

        kvfree(klist);

        return error;
}

static ssize_t path_listxattr(const char __user *pathname, char __user *list,
                              size_t size, unsigned int lookup_flags)
{
        struct path path;
        ssize_t error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = listxattr(path.dentry, list, size);
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
                size_t, size)
{
        return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
                size_t, size)
{
        return path_listxattr(pathname, list, size, 0);
}

SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
{
        struct fd f = fdget(fd);
        ssize_t error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = listxattr(f.file->f_path.dentry, list, size);
        fdput(f);
        return error;
}

/*
 * Extended attribute REMOVE operations
 */
static long
removexattr(struct mnt_idmap *idmap, struct dentry *d,
            const char __user *name)
{
        int error;
        char kname[XATTR_NAME_MAX + 1];

        error = strncpy_from_user(kname, name, sizeof(kname));
        if (error == 0 || error == sizeof(kname))
                error = -ERANGE;
        if (error < 0)
                return error;

        if (is_posix_acl_xattr(kname))
                return vfs_remove_acl(mnt_idmap_owner(idmap), d, kname);

        return vfs_removexattr(mnt_idmap_owner(idmap), d, kname);
}

static int path_removexattr(const char __user *pathname,
                            const char __user *name, unsigned int lookup_flags)
{
        struct path path;
        int error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = mnt_want_write(path.mnt);
        if (!error) {
                error = removexattr(mnt_idmap(path.mnt), path.dentry, name);
                mnt_drop_write(path.mnt);
        }
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
                const char __user *, name)
{
        return path_removexattr(pathname, name, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
                const char __user *, name)
{
        return path_removexattr(pathname, name, 0);
}

SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = mnt_want_write_file(f.file);
        if (!error) {
                error = removexattr(file_mnt_idmap(f.file),
                                    f.file->f_path.dentry, name);
                mnt_drop_write_file(f.file);
        }
        fdput(f);
        return error;
}

/*
 * Combine the results of the list() operation from every xattr_handler in the
 * list.
 */
ssize_t
generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
{
        const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
        unsigned int size = 0;

        if (!buffer) {
                for_each_xattr_handler(handlers, handler) {
                        if (!handler->name ||
                            (handler->list && !handler->list(dentry)))
                                continue;
                        size += strlen(handler->name) + 1;
                }
        } else {
                char *buf = buffer;
                size_t len;

                for_each_xattr_handler(handlers, handler) {
                        if (!handler->name ||
                            (handler->list && !handler->list(dentry)))
                                continue;
                        len = strlen(handler->name);
                        if (len + 1 > buffer_size)
                                return -ERANGE;
                        memcpy(buf, handler->name, len + 1);
                        buf += len + 1;
                        buffer_size -= len + 1;
                }
                size = buf - buffer;
        }
        return size;
}
EXPORT_SYMBOL(generic_listxattr);

/**
 * xattr_full_name  -  Compute full attribute name from suffix
 *
 * @handler:    handler of the xattr_handler operation
 * @name:       name passed to the xattr_handler operation
 *
 * The get and set xattr handler operations are called with the remainder of
 * the attribute name after skipping the handler's prefix: for example, "foo"
 * is passed to the get operation of a handler with prefix "user." to get
 * attribute "user.foo".  The full name is still "there" in the name though.
 *
 * Note: the list xattr handler operation when called from the vfs is passed a
 * NULL name; some file systems use this operation internally, with varying
 * semantics.
 */
const char *xattr_full_name(const struct xattr_handler *handler,
                            const char *name)
{
        size_t prefix_len = strlen(xattr_prefix(handler));

        return name - prefix_len;
}
EXPORT_SYMBOL(xattr_full_name);

/**
 * free_simple_xattr - free an xattr object
 * @xattr: the xattr object
 *
 * Free the xattr object. Can handle @xattr being NULL.
 */
static inline void free_simple_xattr(struct simple_xattr *xattr)
{
        if (xattr)
                kfree(xattr->name);
        kvfree(xattr);
}

/**
 * simple_xattr_alloc - allocate new xattr object
 * @value: value of the xattr object
 * @size: size of @value
 *
 * Allocate a new xattr object and initialize respective members. The caller is
 * responsible for handling the name of the xattr.
 *
 * Return: On success a new xattr object is returned. On failure NULL is
 * returned.
 */
struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
{
        struct simple_xattr *new_xattr;
        size_t len;

        /* wrap around? */
        len = sizeof(*new_xattr) + size;
        if (len < sizeof(*new_xattr))
                return NULL;

        new_xattr = kvmalloc(len, GFP_KERNEL);
        if (!new_xattr)
                return NULL;

        new_xattr->size = size;
        memcpy(new_xattr->value, value, size);
        return new_xattr;
}

/**
 * rbtree_simple_xattr_cmp - compare xattr name with current rbtree xattr entry
 * @key: xattr name
 * @node: current node
 *
 * Compare the xattr name with the xattr name attached to @node in the rbtree.
 *
 * Return: Negative value if continuing left, positive if continuing right, 0
 * if the xattr attached to @node matches @key.
 */
static int rbtree_simple_xattr_cmp(const void *key, const struct rb_node *node)
{
        const char *xattr_name = key;
        const struct simple_xattr *xattr;

        xattr = rb_entry(node, struct simple_xattr, rb_node);
        return strcmp(xattr->name, xattr_name);
}

/**
 * rbtree_simple_xattr_node_cmp - compare two xattr rbtree nodes
 * @new_node: new node
 * @node: current node
 *
 * Compare the xattr attached to @new_node with the xattr attached to @node.
 *
 * Return: Negative value if continuing left, positive if continuing right, 0
 * if the xattr attached to @new_node matches the xattr attached to @node.
 */
static int rbtree_simple_xattr_node_cmp(struct rb_node *new_node,
                                        const struct rb_node *node)
{
        struct simple_xattr *xattr;
        xattr = rb_entry(new_node, struct simple_xattr, rb_node);
        return rbtree_simple_xattr_cmp(xattr->name, node);
}

/**
 * simple_xattr_get - get an xattr object
 * @xattrs: the header of the xattr object
 * @name: the name of the xattr to retrieve
 * @buffer: the buffer to store the value into
 * @size: the size of @buffer
 *
 * Try to find and retrieve the xattr object associated with @name.
 * If @buffer is provided store the value of @xattr in @buffer
 * otherwise just return the length. The size of @buffer is limited
 * to XATTR_SIZE_MAX which currently is 65536.
 *
 * Return: On success the length of the xattr value is returned. On error a
 * negative error code is returned.
 */
int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
                     void *buffer, size_t size)
{
        struct simple_xattr *xattr = NULL;
        struct rb_node *rbp;
        int ret = -ENODATA;

        read_lock(&xattrs->lock);
        rbp = rb_find(name, &xattrs->rb_root, rbtree_simple_xattr_cmp);
        if (rbp) {
                xattr = rb_entry(rbp, struct simple_xattr, rb_node);
                ret = xattr->size;
                if (buffer) {
                        if (size < xattr->size)
                                ret = -ERANGE;
                        else
                                memcpy(buffer, xattr->value, xattr->size);
                }
        }
        read_unlock(&xattrs->lock);
        return ret;
}

/**
 * simple_xattr_set - set an xattr object
 * @xattrs: the header of the xattr object
 * @name: the name of the xattr to retrieve
 * @value: the value to store along the xattr
 * @size: the size of @value
 * @flags: the flags determining how to set the xattr
 * @removed_size: the size of the removed xattr
 *
 * Set a new xattr object.
 * If @value is passed a new xattr object will be allocated. If XATTR_REPLACE
 * is specified in @flags a matching xattr object for @name must already exist.
 * If it does it will be replaced with the new xattr object. If it doesn't we
 * fail. If XATTR_CREATE is specified and a matching xattr does already exist
 * we fail. If it doesn't we create a new xattr. If @flags is zero we simply
 * insert the new xattr replacing any existing one.
 *
 * If @value is empty and a matching xattr object is found we delete it if
 * XATTR_REPLACE is specified in @flags or @flags is zero.
 *
 * If @value is empty and no matching xattr object for @name is found we do
 * nothing if XATTR_CREATE is specified in @flags or @flags is zero. For
 * XATTR_REPLACE we fail as mentioned above.
 *
 * Return: On success zero and on error a negative error code is returned.
 */
int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
                     const void *value, size_t size, int flags,
                     ssize_t *removed_size)
{
        struct simple_xattr *xattr = NULL, *new_xattr = NULL;
        struct rb_node *parent = NULL, **rbp;
        int err = 0, ret;

        if (removed_size)
                *removed_size = -1;

        /* value == NULL means remove */
        if (value) {
                new_xattr = simple_xattr_alloc(value, size);
                if (!new_xattr)
                        return -ENOMEM;

                new_xattr->name = kstrdup(name, GFP_KERNEL);
                if (!new_xattr->name) {
                        free_simple_xattr(new_xattr);
                        return -ENOMEM;
                }
        }

        write_lock(&xattrs->lock);
        rbp = &xattrs->rb_root.rb_node;
        while (*rbp) {
                parent = *rbp;
                ret = rbtree_simple_xattr_cmp(name, *rbp);
                if (ret < 0)
                        rbp = &(*rbp)->rb_left;
                else if (ret > 0)
                        rbp = &(*rbp)->rb_right;
                else
                        xattr = rb_entry(*rbp, struct simple_xattr, rb_node);
                if (xattr)
                        break;
        }

        if (xattr) {
                /* Fail if XATTR_CREATE is requested and the xattr exists. */
                if (flags & XATTR_CREATE) {
                        err = -EEXIST;
                        goto out_unlock;
                }

                if (new_xattr)
                        rb_replace_node(&xattr->rb_node, &new_xattr->rb_node,
                                        &xattrs->rb_root);
                else
                        rb_erase(&xattr->rb_node, &xattrs->rb_root);
                if (!err && removed_size)
                        *removed_size = xattr->size;
        } else {
                /* Fail if XATTR_REPLACE is requested but no xattr is found. */
                if (flags & XATTR_REPLACE) {
                        err = -ENODATA;
                        goto out_unlock;
                }

                /*
                 * If XATTR_CREATE or no flags are specified together with a
                 * new value simply insert it.
                 */
                if (new_xattr) {
                        rb_link_node(&new_xattr->rb_node, parent, rbp);
                        rb_insert_color(&new_xattr->rb_node, &xattrs->rb_root);
                }

                /*
                 * If XATTR_CREATE or no flags are specified and neither an
                 * old or new xattr exist then we don't need to do anything.
                 */
        }

out_unlock:
        write_unlock(&xattrs->lock);
        if (err)
                free_simple_xattr(new_xattr);
        else
                free_simple_xattr(xattr);
        return err;

}

static bool xattr_is_trusted(const char *name)
{
        return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
}

static int xattr_list_one(char **buffer, ssize_t *remaining_size,
                          const char *name)
{
        size_t len = strlen(name) + 1;
        if (*buffer) {
                if (*remaining_size < len)
                        return -ERANGE;
                memcpy(*buffer, name, len);
                *buffer += len;
        }
        *remaining_size -= len;
        return 0;
}

/**
 * simple_xattr_list - list all xattr objects
 * @inode: inode from which to get the xattrs
 * @xattrs: the header of the xattr object
 * @buffer: the buffer to store all xattrs into
 * @size: the size of @buffer
 *
 * List all xattrs associated with @inode. If @buffer is NULL we returned
 * the required size of the buffer. If @buffer is provided we store the
 * xattrs value into it provided it is big enough.
 *
 * Note, the number of xattr names that can be listed with listxattr(2) is
 * limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed
 * then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names
 * are found it will return -E2BIG.
 *
 * Return: On success the required size or the size of the copied xattrs is
 * returned. On error a negative error code is returned.
 */
ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
                          char *buffer, size_t size)
{
        bool trusted = ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
        struct simple_xattr *xattr;
        struct rb_node *rbp;
        ssize_t remaining_size = size;
        int err = 0;

#ifdef CONFIG_FS_POSIX_ACL
        if (IS_POSIXACL(inode)) {
                if (inode->i_acl) {
                        err = xattr_list_one(&buffer, &remaining_size,
                                             XATTR_NAME_POSIX_ACL_ACCESS);
                        if (err)
                                return err;
                }
                if (inode->i_default_acl) {
                        err = xattr_list_one(&buffer, &remaining_size,
                                             XATTR_NAME_POSIX_ACL_DEFAULT);
                        if (err)
                                return err;
                }
        }
#endif

        read_lock(&xattrs->lock);
        for (rbp = rb_first(&xattrs->rb_root); rbp; rbp = rb_next(rbp)) {
                xattr = rb_entry(rbp, struct simple_xattr, rb_node);

                /* skip "trusted." attributes for unprivileged callers */
                if (!trusted && xattr_is_trusted(xattr->name))
                        continue;

                err = xattr_list_one(&buffer, &remaining_size, xattr->name);
                if (err)
                        break;
        }
        read_unlock(&xattrs->lock);

        return err ? err : size - remaining_size;
}

/**
 * rbtree_simple_xattr_less - compare two xattr rbtree nodes
 * @new_node: new node
 * @node: current node
 *
 * Compare the xattr attached to @new_node with the xattr attached to @node.
 * Note that this function technically tolerates duplicate entries.
 *
 * Return: True if insertion point in the rbtree is found.
 */
static bool rbtree_simple_xattr_less(struct rb_node *new_node,
                                     const struct rb_node *node)
{
        return rbtree_simple_xattr_node_cmp(new_node, node) < 0;
}

/**
 * simple_xattr_add - add xattr objects
 * @xattrs: the header of the xattr object
 * @new_xattr: the xattr object to add
 *
 * Add an xattr object to @xattrs. This assumes no replacement or removal
 * of matching xattrs is wanted. Should only be called during inode
 * initialization when a few distinct initial xattrs are supposed to be set.
 */
void simple_xattr_add(struct simple_xattrs *xattrs,
                      struct simple_xattr *new_xattr)
{
        write_lock(&xattrs->lock);
        rb_add(&new_xattr->rb_node, &xattrs->rb_root, rbtree_simple_xattr_less);
        write_unlock(&xattrs->lock);
}

/**
 * simple_xattrs_init - initialize new xattr header
 * @xattrs: header to initialize
 *
 * Initialize relevant fields of a an xattr header.
 */
void simple_xattrs_init(struct simple_xattrs *xattrs)
{
        xattrs->rb_root = RB_ROOT;
        rwlock_init(&xattrs->lock);
}

/**
 * simple_xattrs_free - free xattrs
 * @xattrs: xattr header whose xattrs to destroy
 *
 * Destroy all xattrs in @xattr. When this is called no one can hold a
 * reference to any of the xattrs anymore.
 */
void simple_xattrs_free(struct simple_xattrs *xattrs)
{
        struct rb_node *rbp;

        rbp = rb_first(&xattrs->rb_root);
        while (rbp) {
                struct simple_xattr *xattr;
                struct rb_node *rbp_next;

                rbp_next = rb_next(rbp);
                xattr = rb_entry(rbp, struct simple_xattr, rb_node);
                rb_erase(&xattr->rb_node, &xattrs->rb_root);
                free_simple_xattr(xattr);
                rbp = rbp_next;
        }
}