linux-kernel - [PATCH 3.16.y-ckt 166/185] Btrfs: lock superblock before remounting for rw subvol

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1436951580-15977-167-git-send-email-luis.henriques@canonical.com>
Date:	Wed, 15 Jul 2015 10:12:41 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Omar Sandoval <osandov@...ndov.com>, Chris Mason <clm@...com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 166/185] Btrfs: lock superblock before remounting for rw subvol

3.16.7-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Omar Sandoval <osandov@...ndov.com>

commit 773cd04ec1911abb33cf9538b65f55b76cad5d92 upstream.

Since commit 0723a0473fb4 ("btrfs: allow mounting btrfs subvolumes with
different ro/rw options"), when mounting a subvolume read/write when
another subvolume has previously been mounted read-only, we first do a
remount. However, this should be done with the superblock locked, as per
sync_filesystem():

	/*
	 * We need to be protected against the filesystem going from
	 * r/o to r/w or vice versa.
	 */
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

This WARN_ON can easily be hit with:

mkfs.btrfs -f /dev/vdb
mount /dev/vdb /mnt
btrfs subvol create /mnt/vol1
btrfs subvol create /mnt/vol2
umount /mnt
mount -oro,subvol=/vol1 /dev/vdb /mnt
mount -orw,subvol=/vol2 /dev/vdb /mnt2

Fixes: 0723a0473fb4 ("btrfs: allow mounting btrfs subvolumes with different ro/rw options")
Reviewed-by: David Sterba <dsterba@...e.cz>
Signed-off-by: Omar Sandoval <osandov@...ndov.com>
Signed-off-by: Chris Mason <clm@...com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/btrfs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 600035120ca3..863f3d65fe39 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1203,7 +1203,9 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
 				return ERR_CAST(mnt);
 			}
 
+			down_write(&mnt->mnt_sb->s_umount);
 			r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
+			up_write(&mnt->mnt_sb->s_umount);
 			if (r < 0) {
 				/* FIXME: release vfsmount mnt ??*/
 				kfree(newargs);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/