Btrfs: fix use-after-free in __btrfs_end_transaction

49b25e0540904be0bf558b84475c69d72e4de66e introduced a use-after-free bug
that caused spurious -EIO's to be returned.

Do the check before we free the transaction.

Cc: David Sterba <dsterba@suse.cz>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 8da29e8e4de15999397f137825bb378c2e983ede..11b77a59db629923368f993b3a3b5f6e7a883f15 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -480,6 +480,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
        struct btrfs_transaction *cur_trans = trans->transaction;
        struct btrfs_fs_info *info = root->fs_info;
        int count = 0;
+       int err = 0;
 
        if (--trans->use_count) {
                trans->block_rsv = trans->orig_rsv;
@@ -532,18 +533,18 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 
        if (current->journal_info == trans)
                current->journal_info = NULL;
-       memset(trans, 0, sizeof(*trans));
-       kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
        if (throttle)
                btrfs_run_delayed_iputs(root);
 
        if (trans->aborted ||
            root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
-               return -EIO;
+               err = -EIO;
        }
 
-       return 0;
+       memset(trans, 0, sizeof(*trans));
+       kmem_cache_free(btrfs_trans_handle_cachep, trans);
+       return err;
 }
 
 int btrfs_end_transaction(struct btrfs_trans_handle *trans,