Merge tag 'for-linus-20170825' of git://git.infradead.org/linux-mtd

[mirror_ubuntu-artful-kernel.git] / fs / overlayfs / inode.c

/*
 *
 * Copyright (C) 2011 Novell Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/xattr.h>
#include <linux/posix_acl.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

int ovl_setattr(struct dentry *dentry, struct iattr *attr)
{
        int err;
        struct dentry *upperdentry;
        const struct cred *old_cred;

        /*
         * Check for permissions before trying to copy-up.  This is redundant
         * since it will be rechecked later by ->setattr() on upper dentry.  But
         * without this, copy-up can be triggered by just about anybody.
         *
         * We don't initialize inode->size, which just means that
         * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
         * check for a swapfile (which this won't be anyway).
         */
        err = setattr_prepare(dentry, attr);
        if (err)
                return err;

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        err = ovl_copy_up(dentry);
        if (!err) {
                upperdentry = ovl_dentry_upper(dentry);

                if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
                        attr->ia_valid &= ~ATTR_MODE;

                inode_lock(upperdentry->d_inode);
                old_cred = ovl_override_creds(dentry->d_sb);
                err = notify_change(upperdentry, attr, NULL);
                revert_creds(old_cred);
                if (!err)
                        ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
                inode_unlock(upperdentry->d_inode);
        }
        ovl_drop_write(dentry);
out:
        return err;
}

int ovl_getattr(const struct path *path, struct kstat *stat,
                u32 request_mask, unsigned int flags)
{
        struct dentry *dentry = path->dentry;
        enum ovl_path_type type;
        struct path realpath;
        const struct cred *old_cred;
        bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
        int err;

        type = ovl_path_real(dentry, &realpath);
        old_cred = ovl_override_creds(dentry->d_sb);
        err = vfs_getattr(&realpath, stat, request_mask, flags);
        if (err)
                goto out;

        /*
         * When all layers are on the same fs, all real inode number are
         * unique, so we use the overlay st_dev, which is friendly to du -x.
         *
         * We also use st_ino of the copy up origin, if we know it.
         * This guaranties constant st_dev/st_ino across copy up.
         *
         * If filesystem supports NFS export ops, this also guaranties
         * persistent st_ino across mount cycle.
         */
        if (ovl_same_sb(dentry->d_sb)) {
                if (OVL_TYPE_ORIGIN(type)) {
                        struct kstat lowerstat;
                        u32 lowermask = STATX_INO | (!is_dir ? STATX_NLINK : 0);

                        ovl_path_lower(dentry, &realpath);
                        err = vfs_getattr(&realpath, &lowerstat,
                                          lowermask, flags);
                        if (err)
                                goto out;

                        WARN_ON_ONCE(stat->dev != lowerstat.dev);
                        /*
                         * Lower hardlinks may be broken on copy up to different
                         * upper files, so we cannot use the lower origin st_ino
                         * for those different files, even for the same fs case.
                         * With inodes index enabled, it is safe to use st_ino
                         * of an indexed hardlinked origin. The index validates
                         * that the upper hardlink is not broken.
                         */
                        if (is_dir || lowerstat.nlink == 1 ||
                            ovl_test_flag(OVL_INDEX, d_inode(dentry)))
                                stat->ino = lowerstat.ino;
                }
                stat->dev = dentry->d_sb->s_dev;
        } else if (is_dir) {
                /*
                 * If not all layers are on the same fs the pair {real st_ino;
                 * overlay st_dev} is not unique, so use the non persistent
                 * overlay st_ino.
                 *
                 * Always use the overlay st_dev for directories, so 'find
                 * -xdev' will scan the entire overlay mount and won't cross the
                 * overlay mount boundaries.
                 */
                stat->dev = dentry->d_sb->s_dev;
                stat->ino = dentry->d_inode->i_ino;
        }

        /*
         * It's probably not worth it to count subdirs to get the
         * correct link count.  nlink=1 seems to pacify 'find' and
         * other utilities.
         */
        if (is_dir && OVL_TYPE_MERGE(type))
                stat->nlink = 1;

        /*
         * Return the overlay inode nlinks for indexed upper inodes.
         * Overlay inode nlink counts the union of the upper hardlinks
         * and non-covered lower hardlinks. It does not include the upper
         * index hardlink.
         */
        if (!is_dir && ovl_test_flag(OVL_INDEX, d_inode(dentry)))
                stat->nlink = dentry->d_inode->i_nlink;

out:
        revert_creds(old_cred);

        return err;
}

int ovl_permission(struct inode *inode, int mask)
{
        struct inode *upperinode = ovl_inode_upper(inode);
        struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
        const struct cred *old_cred;
        int err;

        /* Careful in RCU walk mode */
        if (!realinode) {
                WARN_ON(!(mask & MAY_NOT_BLOCK));
                return -ECHILD;
        }

        /*
         * Check overlay inode with the creds of task and underlying inode
         * with creds of mounter
         */
        err = generic_permission(inode, mask);
        if (err)
                return err;

        old_cred = ovl_override_creds(inode->i_sb);
        if (!upperinode &&
            !special_file(realinode->i_mode) && mask & MAY_WRITE) {
                mask &= ~(MAY_WRITE | MAY_APPEND);
                /* Make sure mounter can read file for copy up later */
                mask |= MAY_READ;
        }
        err = inode_permission(realinode, mask);
        revert_creds(old_cred);

        return err;
}

static const char *ovl_get_link(struct dentry *dentry,
                                struct inode *inode,
                                struct delayed_call *done)
{
        const struct cred *old_cred;
        const char *p;

        if (!dentry)
                return ERR_PTR(-ECHILD);

        old_cred = ovl_override_creds(dentry->d_sb);
        p = vfs_get_link(ovl_dentry_real(dentry), done);
        revert_creds(old_cred);
        return p;
}

bool ovl_is_private_xattr(const char *name)
{
        return strncmp(name, OVL_XATTR_PREFIX,
                       sizeof(OVL_XATTR_PREFIX) - 1) == 0;
}

int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
                  const void *value, size_t size, int flags)
{
        int err;
        struct dentry *upperdentry = ovl_i_dentry_upper(inode);
        struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
        const struct cred *old_cred;

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        if (!value && !upperdentry) {
                err = vfs_getxattr(realdentry, name, NULL, 0);
                if (err < 0)
                        goto out_drop_write;
        }

        if (!upperdentry) {
                err = ovl_copy_up(dentry);
                if (err)
                        goto out_drop_write;

                realdentry = ovl_dentry_upper(dentry);
        }

        old_cred = ovl_override_creds(dentry->d_sb);
        if (value)
                err = vfs_setxattr(realdentry, name, value, size, flags);
        else {
                WARN_ON(flags != XATTR_REPLACE);
                err = vfs_removexattr(realdentry, name);
        }
        revert_creds(old_cred);

out_drop_write:
        ovl_drop_write(dentry);
out:
        return err;
}

int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
                  void *value, size_t size)
{
        ssize_t res;
        const struct cred *old_cred;
        struct dentry *realdentry =
                ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);

        old_cred = ovl_override_creds(dentry->d_sb);
        res = vfs_getxattr(realdentry, name, value, size);
        revert_creds(old_cred);
        return res;
}

static bool ovl_can_list(const char *s)
{
        /* List all non-trusted xatts */
        if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
                return true;

        /* Never list trusted.overlay, list other trusted for superuser only */
        return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
}

ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
{
        struct dentry *realdentry = ovl_dentry_real(dentry);
        ssize_t res;
        size_t len;
        char *s;
        const struct cred *old_cred;

        old_cred = ovl_override_creds(dentry->d_sb);
        res = vfs_listxattr(realdentry, list, size);
        revert_creds(old_cred);
        if (res <= 0 || size == 0)
                return res;

        /* filter out private xattrs */
        for (s = list, len = res; len;) {
                size_t slen = strnlen(s, len) + 1;

                /* underlying fs providing us with an broken xattr list? */
                if (WARN_ON(slen > len))
                        return -EIO;

                len -= slen;
                if (!ovl_can_list(s)) {
                        res -= slen;
                        memmove(s, s + slen, len);
                } else {
                        s += slen;
                }
        }

        return res;
}

struct posix_acl *ovl_get_acl(struct inode *inode, int type)
{
        struct inode *realinode = ovl_inode_real(inode);
        const struct cred *old_cred;
        struct posix_acl *acl;

        if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
                return NULL;

        old_cred = ovl_override_creds(inode->i_sb);
        acl = get_acl(realinode, type);
        revert_creds(old_cred);

        return acl;
}

static bool ovl_open_need_copy_up(struct dentry *dentry, int flags)
{
        if (ovl_dentry_upper(dentry) &&
            ovl_dentry_has_upper_alias(dentry))
                return false;

        if (special_file(d_inode(dentry)->i_mode))
                return false;

        if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
                return false;

        return true;
}

int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
{
        int err = 0;

        if (ovl_open_need_copy_up(dentry, file_flags)) {
                err = ovl_want_write(dentry);
                if (!err) {
                        err = ovl_copy_up_flags(dentry, file_flags);
                        ovl_drop_write(dentry);
                }
        }

        return err;
}

int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
{
        struct dentry *alias;
        struct path upperpath;

        if (!(flags & S_ATIME))
                return 0;

        alias = d_find_any_alias(inode);
        if (!alias)
                return 0;

        ovl_path_upper(alias, &upperpath);
        if (upperpath.dentry) {
                touch_atime(&upperpath);
                inode->i_atime = d_inode(upperpath.dentry)->i_atime;
        }

        dput(alias);

        return 0;
}

static const struct inode_operations ovl_file_inode_operations = {
        .setattr        = ovl_setattr,
        .permission     = ovl_permission,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .get_acl        = ovl_get_acl,
        .update_time    = ovl_update_time,
};

static const struct inode_operations ovl_symlink_inode_operations = {
        .setattr        = ovl_setattr,
        .get_link       = ovl_get_link,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .update_time    = ovl_update_time,
};

/*
 * It is possible to stack overlayfs instance on top of another
 * overlayfs instance as lower layer. We need to annonate the
 * stackable i_mutex locks according to stack level of the super
 * block instance. An overlayfs instance can never be in stack
 * depth 0 (there is always a real fs below it).  An overlayfs
 * inode lock will use the lockdep annotaion ovl_i_mutex_key[depth].
 *
 * For example, here is a snip from /proc/lockdep_chains after
 * dir_iterate of nested overlayfs:
 *
 * [...] &ovl_i_mutex_dir_key[depth]   (stack_depth=2)
 * [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1)
 * [...] &type->i_mutex_dir_key        (stack_depth=0)
 */
#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH

static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
{
#ifdef CONFIG_LOCKDEP
        static struct lock_class_key ovl_i_mutex_key[OVL_MAX_NESTING];
        static struct lock_class_key ovl_i_mutex_dir_key[OVL_MAX_NESTING];

        int depth = inode->i_sb->s_stack_depth - 1;

        if (WARN_ON_ONCE(depth < 0 || depth >= OVL_MAX_NESTING))
                depth = 0;

        if (S_ISDIR(inode->i_mode))
                lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_dir_key[depth]);
        else
                lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_key[depth]);
#endif
}

static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
        inode->i_ino = get_next_ino();
        inode->i_mode = mode;
        inode->i_flags |= S_NOCMTIME;
#ifdef CONFIG_FS_POSIX_ACL
        inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
#endif

        ovl_lockdep_annotate_inode_mutex_key(inode);

        switch (mode & S_IFMT) {
        case S_IFREG:
                inode->i_op = &ovl_file_inode_operations;
                break;

        case S_IFDIR:
                inode->i_op = &ovl_dir_inode_operations;
                inode->i_fop = &ovl_dir_operations;
                break;

        case S_IFLNK:
                inode->i_op = &ovl_symlink_inode_operations;
                break;

        default:
                inode->i_op = &ovl_file_inode_operations;
                init_special_inode(inode, mode, rdev);
                break;
        }
}

/*
 * With inodes index enabled, an overlay inode nlink counts the union of upper
 * hardlinks and non-covered lower hardlinks. During the lifetime of a non-pure
 * upper inode, the following nlink modifying operations can happen:
 *
 * 1. Lower hardlink copy up
 * 2. Upper hardlink created, unlinked or renamed over
 * 3. Lower hardlink whiteout or renamed over
 *
 * For the first, copy up case, the union nlink does not change, whether the
 * operation succeeds or fails, but the upper inode nlink may change.
 * Therefore, before copy up, we store the union nlink value relative to the
 * lower inode nlink in the index inode xattr trusted.overlay.nlink.
 *
 * For the second, upper hardlink case, the union nlink should be incremented
 * or decremented IFF the operation succeeds, aligned with nlink change of the
 * upper inode. Therefore, before link/unlink/rename, we store the union nlink
 * value relative to the upper inode nlink in the index inode.
 *
 * For the last, lower cover up case, we simplify things by preceding the
 * whiteout or cover up with copy up. This makes sure that there is an index
 * upper inode where the nlink xattr can be stored before the copied up upper
 * entry is unlink.
 */
#define OVL_NLINK_ADD_UPPER     (1 << 0)

/*
 * On-disk format for indexed nlink:
 *
 * nlink relative to the upper inode - "U[+-]NUM"
 * nlink relative to the lower inode - "L[+-]NUM"
 */

static int ovl_set_nlink_common(struct dentry *dentry,
                                struct dentry *realdentry, const char *format)
{
        struct inode *inode = d_inode(dentry);
        struct inode *realinode = d_inode(realdentry);
        char buf[13];
        int len;

        len = snprintf(buf, sizeof(buf), format,
                       (int) (inode->i_nlink - realinode->i_nlink));

        return ovl_do_setxattr(ovl_dentry_upper(dentry),
                               OVL_XATTR_NLINK, buf, len, 0);
}

int ovl_set_nlink_upper(struct dentry *dentry)
{
        return ovl_set_nlink_common(dentry, ovl_dentry_upper(dentry), "U%+i");
}

int ovl_set_nlink_lower(struct dentry *dentry)
{
        return ovl_set_nlink_common(dentry, ovl_dentry_lower(dentry), "L%+i");
}

unsigned int ovl_get_nlink(struct dentry *lowerdentry,
                           struct dentry *upperdentry,
                           unsigned int fallback)
{
        int nlink_diff;
        int nlink;
        char buf[13];
        int err;

        if (!lowerdentry || !upperdentry || d_inode(lowerdentry)->i_nlink == 1)
                return fallback;

        err = vfs_getxattr(upperdentry, OVL_XATTR_NLINK, &buf, sizeof(buf) - 1);
        if (err < 0)
                goto fail;

        buf[err] = '\0';
        if ((buf[0] != 'L' && buf[0] != 'U') ||
            (buf[1] != '+' && buf[1] != '-'))
                goto fail;

        err = kstrtoint(buf + 1, 10, &nlink_diff);
        if (err < 0)
                goto fail;

        nlink = d_inode(buf[0] == 'L' ? lowerdentry : upperdentry)->i_nlink;
        nlink += nlink_diff;

        if (nlink <= 0)
                goto fail;

        return nlink;

fail:
        pr_warn_ratelimited("overlayfs: failed to get index nlink (%pd2, err=%i)\n",
                            upperdentry, err);
        return fallback;
}

struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
{
        struct inode *inode;

        inode = new_inode(sb);
        if (inode)
                ovl_fill_inode(inode, mode, rdev);

        return inode;
}

static int ovl_inode_test(struct inode *inode, void *data)
{
        return inode->i_private == data;
}

static int ovl_inode_set(struct inode *inode, void *data)
{
        inode->i_private = data;
        return 0;
}

static bool ovl_verify_inode(struct inode *inode, struct dentry *lowerdentry,
                             struct dentry *upperdentry)
{
        struct inode *lowerinode = lowerdentry ? d_inode(lowerdentry) : NULL;

        /* Lower (origin) inode must match, even if NULL */
        if (ovl_inode_lower(inode) != lowerinode)
                return false;

        /*
         * Allow non-NULL __upperdentry in inode even if upperdentry is NULL.
         * This happens when finding a lower alias for a copied up hard link.
         */
        if (upperdentry && ovl_inode_upper(inode) != d_inode(upperdentry))
                return false;

        return true;
}

struct inode *ovl_get_inode(struct dentry *dentry, struct dentry *upperdentry)
{
        struct dentry *lowerdentry = ovl_dentry_lower(dentry);
        struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
        struct inode *inode;

        if (!realinode)
                realinode = d_inode(lowerdentry);

        if (!S_ISDIR(realinode->i_mode) &&
            (upperdentry || (lowerdentry && ovl_indexdir(dentry->d_sb)))) {
                struct inode *key = d_inode(lowerdentry ?: upperdentry);
                unsigned int nlink;

                inode = iget5_locked(dentry->d_sb, (unsigned long) key,
                                     ovl_inode_test, ovl_inode_set, key);
                if (!inode)
                        goto out_nomem;
                if (!(inode->i_state & I_NEW)) {
                        /*
                         * Verify that the underlying files stored in the inode
                         * match those in the dentry.
                         */
                        if (!ovl_verify_inode(inode, lowerdentry, upperdentry)) {
                                iput(inode);
                                inode = ERR_PTR(-ESTALE);
                                goto out;
                        }

                        dput(upperdentry);
                        goto out;
                }

                nlink = ovl_get_nlink(lowerdentry, upperdentry,
                                      realinode->i_nlink);
                set_nlink(inode, nlink);
        } else {
                inode = new_inode(dentry->d_sb);
                if (!inode)
                        goto out_nomem;
        }
        ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
        ovl_inode_init(inode, upperdentry, lowerdentry);

        if (upperdentry && ovl_is_impuredir(upperdentry))
                ovl_set_flag(OVL_IMPURE, inode);

        if (inode->i_state & I_NEW)
                unlock_new_inode(inode);
out:
        return inode;

out_nomem:
        inode = ERR_PTR(-ENOMEM);
        goto out;
}