btrfs: relocation: set trans to be NULL after ending transaction
authorPan Bian <bianpan2016@163.com>
Fri, 23 Nov 2018 10:10:15 +0000 (18:10 +0800)
committerDavid Sterba <dsterba@suse.com>
Fri, 23 Nov 2018 12:47:46 +0000 (13:47 +0100)
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>
fs/btrfs/relocation.c

index 924116f654a110cb9e23a878002bed0ae967029e..a3f75b8926d4474aa1093ffdd852d422b853e2d2 100644 (file)
@@ -3959,6 +3959,7 @@ 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);
 restart:
                if (update_backref_cache(trans, &rc->backref_cache)) {
                        btrfs_end_transaction(trans);
+                       trans = NULL;
                        continue;
                }
 
                        continue;
                }