[PATCH AUTOSEL 4.18 06/76] btrfs: btrfs_shrink_device should call commit transaction at the end

[Sasha Levin]

From: Anand Jain <anand.jain@xxxxxxxxxx>

[ Upstream commit 801660b040d132f67fac6a95910ad307c5929b49 ]

Test case btrfs/164 reports use-after-free:

[ 6712.084324] general protection fault: 0000 [#1] PREEMPT SMP
..
[ 6712.195423]  btrfs_update_commit_device_size+0x75/0xf0 [btrfs]
[ 6712.201424]  btrfs_commit_transaction+0x57d/0xa90 [btrfs]
[ 6712.206999]  btrfs_rm_device+0x627/0x850 [btrfs]
[ 6712.211800]  btrfs_ioctl+0x2b03/0x3120 [btrfs]

Reason for this is that btrfs_shrink_device adds the resized device to
the fs_devices::resized_devices after it has called the last commit
transaction.

So the list fs_devices::resized_devices is not empty when
btrfs_shrink_device returns.  Now the parent function
btrfs_rm_device calls:

        btrfs_close_bdev(device);
        call_rcu(&device->rcu, free_device_rcu);

and then does the transactio ncommit. It goes through the
fs_devices::resized_devices in btrfs_update_commit_device_size and
leads to use-after-free.

Fix this by making sure btrfs_shrink_device calls the last needed
btrfs_commit_transaction before the return. This is consistent with what
the grow counterpart does and this makes sure the on-disk state is
persistent when the function returns.

Reported-by: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>
Tested-by: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>
Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 fs/btrfs/volumes.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5304b8d6ceb8..1a22c0ecaf67 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4584,7 +4584,12 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 
 	/* Now btrfs_update_device() will change the on-disk size. */
 	ret = btrfs_update_device(trans, device);
-	btrfs_end_transaction(trans);
+	if (ret < 0) {
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+	} else {
+		ret = btrfs_commit_transaction(trans);
+	}
 done:
 	btrfs_free_path(path);
 	if (ret) {
-- 
2.17.1