btrfs: relocation: set trans to be NULL after ending transaction

commit 42a657f57628402c73237547f0134e083e2f6764 upstream.

The function relocate_block_group calls btrfs_end_transaction to release
trans when update_backref_cache returns 1, and then continues the loop
body. If btrfs_block_rsv_refill fails this time, it will jump out the
loop and the freed trans will be accessed. This may result in a
use-after-free bug. The patch assigns NULL to trans after trans is
released so that it will not be accessed.

Fixes: 0647bf564f1 ("Btrfs: improve forever loop when doing balance relocation")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 60bf8df..0526b6c 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3963,6 +3963,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
 restart:
                if (update_backref_cache(trans, &rc->backref_cache)) {
                        btrfs_end_transaction(trans);
+                       trans = NULL;
                        continue;
                }