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>
---
rebased on topf Josef's master branch (which itself is 3.1-based and contains
the vfs_path_lookup API change)
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 934789f..6638e51 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -722,6 +722,16 @@ static int btrfs_set_super(struct super_block *s, void *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;
+}
+
+/*
* This will strip out the subvol=%s argument for an argument string and add
* subvolid=0 to make sure we get the actual tree root for path walking to the
* subvol we want.
@@ -824,6 +834,15 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
if (error)
return ERR_PTR(error);
+ if (!is_subvolume_inode(path.dentry->d_inode)) {
+ path_put(&path);
+ mntput(mnt);
+ error = -EINVAL;
+ printk(KERN_ERR "btrfs: '%s' is not a valid subvolume\n",
+ subvol_name);
+ return ERR_PTR(-EINVAL);
+ }
+
/* Get a ref to the sb and the dentry we found and return it */
s = path.mnt->mnt_sb;
atomic_inc(&s->s_active);
--
1.7.6.233.gd79bc
--
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