Btrfs: allow subvol deletion by unprivileged user with -o user_subvol_rm_allowed

Add a mount option user_subvol_rm_allowed that allows users to delete a
(potentially non-empty!) subvol when they would otherwise we allowed to do
an rmdir(2).  We duplicate the may_delete() checks from the core VFS code
to implement identical security checks (minus the directory size check).
We additionally require that the user has write+exec permission on the
subvol root inode.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e5d66b1..8db9234 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1234,6 +1234,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_FORCE_COMPRESS      (1 << 11)
 #define BTRFS_MOUNT_SPACE_CACHE                (1 << 12)
 #define BTRFS_MOUNT_CLEAR_CACHE                (1 << 13)
+#define BTRFS_MOUNT_USER_SUBVOL_RM_ALLOWED (1 << 14)
 
 #define btrfs_clear_opt(o, opt)                ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)          ((o) |= BTRFS_MOUNT_##opt)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index fdd88f2..463d91b 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -409,6 +409,76 @@ fail:
        return ret;
 }
 
+/*  copy of check_sticky in fs/namei.c()
+* It's inline, so penalty for filesystems that don't use sticky bit is
+* minimal.
+*/
+static inline int btrfs_check_sticky(struct inode *dir, struct inode *inode)
+{
+       uid_t fsuid = current_fsuid();
+
+       if (!(dir->i_mode & S_ISVTX))
+               return 0;
+       if (inode->i_uid == fsuid)
+               return 0;
+       if (dir->i_uid == fsuid)
+               return 0;
+       return !capable(CAP_FOWNER);
+}
+
+/*  copy of may_delete in fs/namei.c()
+ *     Check whether we can remove a link victim from directory dir, check
+ *  whether the type of victim is right.
+ *  1. We can't do it if dir is read-only (done in permission())
+ *  2. We should have write and exec permissions on dir
+ *  3. We can't remove anything from append-only dir
+ *  4. We can't do anything with immutable dir (done in permission())
+ *  5. If the sticky bit on dir is set we should either
+ *     a. be owner of dir, or
+ *     b. be owner of victim, or
+ *     c. have CAP_FOWNER capability
+ *  6. If the victim is append-only or immutable we can't do antyhing with
+ *     links pointing to it.
+ *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
+ *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
+ *  9. We can't remove a root or mountpoint.
+ * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
+ *     nfs_async_unlink().
+ */
+
+static int btrfs_may_delete(struct inode *dir,struct dentry *victim,int isdir)
+{
+       int error;
+
+       if (!victim->d_inode)
+               return -ENOENT;
+
+       BUG_ON(victim->d_parent->d_inode != dir);
+       audit_inode_child(victim, dir);
+
+       error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+       if (error)
+               return error;
+       if (IS_APPEND(dir))
+               return -EPERM;
+       if (btrfs_check_sticky(dir, victim->d_inode)||
+               IS_APPEND(victim->d_inode)||
+           IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
+               return -EPERM;
+       if (isdir) {
+               if (!S_ISDIR(victim->d_inode->i_mode))
+                       return -ENOTDIR;
+               if (IS_ROOT(victim))
+                       return -EBUSY;
+       } else if (S_ISDIR(victim->d_inode->i_mode))
+               return -EISDIR;
+       if (IS_DEADDIR(dir))
+               return -ENOENT;
+       if (victim->d_flags & DCACHE_NFSFS_RENAMED)
+               return -EBUSY;
+       return 0;
+}
+
 /* copy of may_create in fs/namei.c() */
 static inline int btrfs_may_create(struct inode *dir, struct dentry *child)
 {
@@ -1274,9 +1344,6 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
        int ret;
        int err = 0;
 
-       if (!capable(CAP_SYS_ADMIN))
-               return -EPERM;
-
        vol_args = memdup_user(arg, sizeof(*vol_args));
        if (IS_ERR(vol_args))
                return PTR_ERR(vol_args);
@@ -1306,13 +1373,51 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
        }
 
        inode = dentry->d_inode;
+       dest = BTRFS_I(inode)->root;
+       if (!capable(CAP_SYS_ADMIN)){
+               /*
+                * Regular user.  Only allow this with a special mount
+                * option, when the user has write+exec access to the
+                * subvol root, and when rmdir(2) would have been
+                * allowed.
+                *
+                * Note that this is _not_ check that the subvol is
+                * empty or doesn't contain data that we wouldn't
+                * otherwise be able to delete.
+                *
+                * Users who want to delete empty subvols should try
+                * rmdir(2).
+                */
+               err = -EPERM;
+               if (!btrfs_test_opt(root, USER_SUBVOL_RM_ALLOWED))
+                       goto out_dput;
+
+               /*
+                * Do not allow deletion if the parent dir is the same
+                * as the dir to be deleted.  That means the ioctl
+                * must be called on the dentry referencing the root
+                * of the subvol, not a random directory contained
+                * within it.
+                */
+               err = -EINVAL;
+               if (root == dest)
+                       goto out_dput;
+
+               err = inode_permission(inode, MAY_WRITE | MAY_EXEC);
+               if (err)
+                       goto out_dput;
+
+               /* check if subvolume may be deleted by a non-root user */
+               err = btrfs_may_delete(dir, dentry, 1);
+               if (err)
+                       goto out_dput;
+       }
+
        if (inode->i_ino != BTRFS_FIRST_FREE_OBJECTID) {
                err = -EINVAL;
                goto out_dput;
        }
 
-       dest = BTRFS_I(inode)->root;
-
        mutex_lock(&inode->i_mutex);
        err = d_invalidate(dentry);
        if (err)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 0002e6d..718b10d 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -71,6 +71,7 @@ enum {
        Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
        Opt_compress_force, Opt_notreelog, Opt_ratio, Opt_flushoncommit,
        Opt_discard, Opt_space_cache, Opt_clear_cache, Opt_err,
+       Opt_user_subvol_rm_allowed,
 };
 
 static match_table_t tokens = {
@@ -96,6 +97,7 @@ static match_table_t tokens = {
        {Opt_discard, "discard"},
        {Opt_space_cache, "space_cache"},
        {Opt_clear_cache, "clear_cache"},
+       {Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
        {Opt_err, NULL},
 };
 
@@ -246,6 +248,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                        printk(KERN_INFO "btrfs: force clearing of disk cache\n");
                        btrfs_set_opt(info->mount_opt, CLEAR_CACHE);
                        break;
+               case Opt_user_subvol_rm_allowed:
+                       btrfs_set_opt(info->mount_opt, USER_SUBVOL_RM_ALLOWED);
+                       break;
                case Opt_err:
                        printk(KERN_INFO "btrfs: unrecognized mount option "
                               "'%s'\n", p);