UBUNTU: SAUCE: (namespace) fuse: Support fuse filesystems outside of init_user_ns

In order to support mounts from namespaces other than
init_user_ns, fuse must translate uids and gids to/from the
userns of the process servicing requests on /dev/fuse. This
patch does that, with a couple of restrictions on the namespace:

 - The userns for the fuse connection is fixed to the namespace
   from which /dev/fuse is opened.

 - The namespace must be the same as s_user_ns.

These restrictions simplify the implementation by avoiding the
need to pass around userns references and by allowing fuse to
rely on the checks in inode_change_ok for ownership changes.
Either restriction could be relaxed in the future if needed.

For cuse the namespace used for the connection is also simply
current_user_ns() at the time /dev/cuse is opened.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index c5b6b71654893b2bb7fe0276a40ac57ddb3350a0..98ebd0f4fd4c7dacf03b42eda804f6172677bcb5 100644 (file)
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -48,6 +48,7 @@
 #include <linux/stat.h>
 #include <linux/module.h>
 #include <linux/uio.h>
+#include <linux/user_namespace.h>
 
 #include "fuse_i.h"
 
@@ -498,7 +499,7 @@ static int cuse_channel_open(struct inode *inode, struct file *file)
        if (!cc)
                return -ENOMEM;
 
-       fuse_conn_init(&cc->fc);
+       fuse_conn_init(&cc->fc, current_user_ns());
 
        fud = fuse_dev_alloc(&cc->fc);
        if (!fud) {

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index e0a6a4f8dcf0022903f3892ea41a60a74ec88c02..616a8807b07b605f4d46dc5b46cb4f05ea1dacb4 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -114,8 +114,8 @@ static void __fuse_put_request(struct fuse_req *req)
 
 static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
 {
-       req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
-       req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
+       req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
+       req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
        req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 }
 
@@ -167,6 +167,10 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
        __set_bit(FR_WAITING, &req->flags);
        if (for_background)
                __set_bit(FR_BACKGROUND, &req->flags);
+       if (req->in.h.uid == (uid_t)-1 || req->in.h.gid == (gid_t)-1) {
+               fuse_put_request(fc, req);
+               return ERR_PTR(-EOVERFLOW);
+       }
 
        return req;
 
@@ -1223,7 +1227,8 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
        struct fuse_in *in;
        unsigned reqsize;
 
-       if (task_active_pid_ns(current) != fc->pid_ns)
+       if (task_active_pid_ns(current) != fc->pid_ns ||
+           current_user_ns() != fc->user_ns)
                return -EIO;
 
  restart:
@@ -1824,7 +1829,8 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
        struct fuse_req *req;
        struct fuse_out_header oh;
 
-       if (task_active_pid_ns(current) != fc->pid_ns)
+       if (task_active_pid_ns(current) != fc->pid_ns ||
+           current_user_ns() != fc->user_ns)
                return -EIO;
 
        if (nbytes < sizeof(struct fuse_out_header))

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 811fd8929a18c1e330316202fd40ac58857ec3c7..ea24eae8a576b0f0edcd0b81df56660199d0bf17 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -858,8 +858,8 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
        stat->ino = attr->ino;
        stat->mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
        stat->nlink = attr->nlink;
-       stat->uid = make_kuid(&init_user_ns, attr->uid);
-       stat->gid = make_kgid(&init_user_ns, attr->gid);
+       stat->uid = make_kuid(fc->user_ns, attr->uid);
+       stat->gid = make_kgid(fc->user_ns, attr->gid);
        stat->rdev = inode->i_rdev;
        stat->atime.tv_sec = attr->atime;
        stat->atime.tv_nsec = attr->atimensec;
@@ -1478,17 +1478,17 @@ static bool update_mtime(unsigned ivalid, bool trust_local_mtime)
        return true;
 }
 
-static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
-                          bool trust_local_cmtime)
+static void iattr_to_fattr(struct fuse_conn *fc, struct iattr *iattr,
+                          struct fuse_setattr_in *arg, bool trust_local_cmtime)
 {
        unsigned ivalid = iattr->ia_valid;
 
        if (ivalid & ATTR_MODE)
                arg->valid |= FATTR_MODE,   arg->mode = iattr->ia_mode;
        if (ivalid & ATTR_UID)
-               arg->valid |= FATTR_UID,    arg->uid = from_kuid(&init_user_ns, iattr->ia_uid);
+               arg->valid |= FATTR_UID,    arg->uid = from_kuid(fc->user_ns, iattr->ia_uid);
        if (ivalid & ATTR_GID)
-               arg->valid |= FATTR_GID,    arg->gid = from_kgid(&init_user_ns, iattr->ia_gid);
+               arg->valid |= FATTR_GID,    arg->gid = from_kgid(fc->user_ns, iattr->ia_gid);
        if (ivalid & ATTR_SIZE)
                arg->valid |= FATTR_SIZE,   arg->size = iattr->ia_size;
        if (ivalid & ATTR_ATIME) {
@@ -1649,7 +1649,7 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
 
        memset(&inarg, 0, sizeof(inarg));
        memset(&outarg, 0, sizeof(outarg));
-       iattr_to_fattr(attr, &inarg, trust_local_cmtime);
+       iattr_to_fattr(fc, attr, &inarg, trust_local_cmtime);
        if (file) {
                struct fuse_file *ff = file->private_data;
                inarg.valid |= FATTR_FH;

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 2760cc92dc554d70ab3d0bd13816b333f802853d..5ff0dc46a257bab5cfc132b2c2c3024b7830448b 100644 (file)
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -25,6 +25,7 @@
 #include <linux/kref.h>
 #include <linux/xattr.h>
 #include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -465,6 +466,9 @@ struct fuse_conn {
        /** The pid namespace for this mount */
        struct pid_namespace *pid_ns;
 
+       /** The user namespace for this mount */
+       struct user_namespace *user_ns;
+
        /** Maximum read size */
        unsigned max_read;
 
@@ -876,7 +880,7 @@ struct fuse_conn *fuse_conn_get(struct fuse_conn *fc);
 /**
  * Initialize fuse_conn
  */
-void fuse_conn_init(struct fuse_conn *fc);
+void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns);
 
 /**
  * Release reference to fuse_conn

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 5b97ad598dc5898c9b486d161823b334c154dc32..29a8fbeef986def43a5c8284666c19cd8fa15785 100644 (file)
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -171,8 +171,8 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
        inode->i_ino     = fuse_squash_ino(attr->ino);
        inode->i_mode    = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
        set_nlink(inode, attr->nlink);
-       inode->i_uid     = make_kuid(&init_user_ns, attr->uid);
-       inode->i_gid     = make_kgid(&init_user_ns, attr->gid);
+       inode->i_uid     = make_kuid(fc->user_ns, attr->uid);
+       inode->i_gid     = make_kgid(fc->user_ns, attr->gid);
        inode->i_blocks  = attr->blocks;
        inode->i_atime.tv_sec   = attr->atime;
        inode->i_atime.tv_nsec  = attr->atimensec;
@@ -484,7 +484,8 @@ static int fuse_match_uint(substring_t *s, unsigned int *res)
        return err;
 }
 
-static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
+static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
+                         struct user_namespace *user_ns)
 {
        char *p;
        memset(d, 0, sizeof(struct fuse_mount_data));
@@ -520,7 +521,7 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
                case OPT_USER_ID:
                        if (fuse_match_uint(&args[0], &uv))
                                return 0;
-                       d->user_id = make_kuid(current_user_ns(), uv);
+                       d->user_id = make_kuid(user_ns, uv);
                        if (!uid_valid(d->user_id))
                                return 0;
                        d->user_id_present = 1;
@@ -529,7 +530,7 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
                case OPT_GROUP_ID:
                        if (fuse_match_uint(&args[0], &uv))
                                return 0;
-                       d->group_id = make_kgid(current_user_ns(), uv);
+                       d->group_id = make_kgid(user_ns, uv);
                        if (!gid_valid(d->group_id))
                                return 0;
                        d->group_id_present = 1;
@@ -572,8 +573,8 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
        struct super_block *sb = root->d_sb;
        struct fuse_conn *fc = get_fuse_conn_super(sb);
 
-       seq_printf(m, ",user_id=%u", from_kuid_munged(&init_user_ns, fc->user_id));
-       seq_printf(m, ",group_id=%u", from_kgid_munged(&init_user_ns, fc->group_id));
+       seq_printf(m, ",user_id=%u", from_kuid_munged(fc->user_ns, fc->user_id));
+       seq_printf(m, ",group_id=%u", from_kgid_munged(fc->user_ns, fc->group_id));
        if (fc->default_permissions)
                seq_puts(m, ",default_permissions");
        if (fc->allow_other)
@@ -604,7 +605,7 @@ static void fuse_pqueue_init(struct fuse_pqueue *fpq)
        fpq->connected = 1;
 }
 
-void fuse_conn_init(struct fuse_conn *fc)
+void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns)
 {
        memset(fc, 0, sizeof(*fc));
        spin_lock_init(&fc->lock);
@@ -628,6 +629,7 @@ void fuse_conn_init(struct fuse_conn *fc)
        fc->attr_version = 1;
        get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
        fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
+       fc->user_ns = get_user_ns(user_ns);
 }
 EXPORT_SYMBOL_GPL(fuse_conn_init);
 
@@ -637,6 +639,7 @@ void fuse_conn_put(struct fuse_conn *fc)
                if (fc->destroy_req)
                        fuse_request_free(fc->destroy_req);
                put_pid_ns(fc->pid_ns);
+               put_user_ns(fc->user_ns);
                fc->release(fc);
        }
 }
@@ -1069,7 +1072,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 
        sb->s_flags &= ~(MS_NOSEC | MS_I_VERSION);
 
-       if (!parse_fuse_opt(data, &d, is_bdev))
+       if (!parse_fuse_opt(data, &d, is_bdev, sb->s_user_ns))
                goto err;
 
        if (is_bdev) {
@@ -1094,8 +1097,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
        if (!file)
                goto err;
 
-       if ((file->f_op != &fuse_dev_operations) ||
-           (file->f_cred->user_ns != &init_user_ns))
+       /*
+        * Require mount to happen from the same user namespace which
+        * opened /dev/fuse to prevent potential attacks.
+        */
+       if (file->f_op != &fuse_dev_operations ||
+           file->f_cred->user_ns != sb->s_user_ns)
                goto err_fput;
 
        fc = kmalloc(sizeof(*fc), GFP_KERNEL);
@@ -1103,7 +1110,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
        if (!fc)
                goto err_fput;
 
-       fuse_conn_init(fc);
+       fuse_conn_init(fc, sb->s_user_ns);
        fc->release = fuse_free_conn;
 
        fud = fuse_dev_alloc(fc);