jbd2: don't mark block as modified if the handle is out of credits

commit e09463f220ca9a1a1ecfda84fcda658f99a1f12a upstream.

Do not set the b_modified flag in block's journal head should not
until after we're sure that jbd2_journal_dirty_metadat() will not
abort with an error due to there not being enough space reserved in
the jbd2 handle.

Otherwise, future attempts to modify the buffer may lead a large
number of spurious errors and warnings.

This addresses CVE-2018-10883.

https://bugzilla.kernel.org/show_bug.cgi?id=200071

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: Drop the added logging statement, as it's on
 a code path that doesn't exist here]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 3a5c29a5733d4536d3ed7a76f7f608fee8c8b9cb..3ab84e02c6ddf46e49815e7cac741ef9b6f2315e 100644 (file)
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1288,11 +1288,11 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
                 * of the transaction. This needs to be done
                 * once a transaction -bzzz
                 */
-               jh->b_modified = 1;
                if (handle->h_buffer_credits <= 0) {
                        ret = -ENOSPC;
                        goto out_unlock_bh;
                }
+               jh->b_modified = 1;
                handle->h_buffer_credits--;
        }