[PATCH 3.18 116/120] jbd2: dont mark block as modified if the handle is out of credits

Greg Kroah-Hartman
2018-10-11T15:40:57Z

From: Theodore Ts'o <tytso@mit.edu>

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>
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/jbd2/transaction.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1283,11 +1283,11 @@ int jbd2_journal_dirty_metadata(handle_t
* 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--;
}