On Sat, Jul 30, 2011 at 12:16:44AM +0800, Zhong, Xin wrote:

I believe I have submit a similar patch months ago:
http://marc.info/?l=linux-btrfs&m=130208585106572&w=2

You did! I was not aware of that. I believe adding a helper make things
more clear (if it were used all over the code).

Hope it can be integrated this time, :-).

mehopes too,
david

quoted

-----Original Message-----
From: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-
owner@vger.kernel.org] On Behalf Of David Sterba
Sent: Friday, July 29, 2011 6:14 PM
To: linux-btrfs@vger.kernel.org
Cc: chris.mason@oracle.com; David Sterba
Subject: [PATCH] btrfs: do not allow mounting non-subvolumes via subvol
option

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 <redacted>
---

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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