There's a missing test whether the path passed to subvol=path option
during mount is a real subvolume, allowing any directory located in
default subovlume to be passed and accepted for mount.
(current btrfs progs prevent this early)
$ btrfs subvol snapshot . p1-snap
ERROR: '.' is not a subvolume
(with "is subvolume?" test bypassed)
$ btrfs subvol snapshot . p1-snap
Create a snapshot of '.' in './p1-snap'
$ btrfs subvol list -p .
ID 258 parent 5 top level 5 path subvol
ID 259 parent 5 top level 5 path subvol1
ID 260 parent 5 top level 5 path default-subvol1
ID 262 parent 5 top level 5 path p1/p1-snapshot
ID 263 parent 259 top level 5 path subvol1/subvol1-snap
The problem I see is that this makes a false impression of snapshotting the
given subvolume but in fact snapshots the default one: a user expects outcome
like ID 263 but in fact gets ID 262 .
This patch makes mount fail with EINVAL with a message in syslog.
Signed-off-by: David Sterba <dsterba@xxxxxxx>
---
I did not find a better errno than EINVAL, probably adding someting like
ENSUBVOL would be better so that other filesystems with such functionality may
use it in future.
fs/btrfs/super.c | 19 +++++++++++++++++++
1 files changed, 19 insertions(+), 0 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 15634d4..0c2a1d1 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -753,6 +753,15 @@ static int btrfs_set_super(struct super_block *s, void *data)
return set_anon_super(s, data);
}
+/*
+ * subvolumes are identified by ino 256
+ */
+static inline int is_subvolume_inode(struct inode *inode)
+{
+ if (inode && inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
+ return 1;
+ return 0;
+}
/*
* Find a superblock for the given device / mount point.
@@ -873,6 +882,16 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
error = -ENXIO;
goto error_free_subvol_name;
}
+
+ if (!is_subvolume_inode(new_root->d_inode)) {
+ dput(root);
+ dput(new_root);
+ deactivate_locked_super(s);
+ error = -EINVAL;
+ printk(KERN_ERR "btrfs: '%s' is not a valid subvolume\n",
+ subvol_name);
+ goto error_free_subvol_name;
+ }
dput(root);
root = new_root;
} else {
--
1.7.6
--
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