Commit 3152fcd4 authored Nov 05, 2019 by Jan Kara Committed by Greg Kroah-Hartman Dec 13, 2019

jbd2: Fix possible overflow in jbd2_log_space_left()



commit add3efdd78b8a0478ce423bb9d4df6bd95e8b335 upstream.

When number of free space in the journal is very low, the arithmetic in
jbd2_log_space_left() could underflow resulting in very high number of
free blocks and thus triggering assertion failure in transaction commit
code complaining there's not enough space in the journal:

J_ASSERT(journal->j_free > 1);

Properly check for the low number of free blocks.

CC: stable@vger.kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191105164437.32602-1-jack@suse.cz


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 18493bac

include/linux/jbd2.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -1587,7 +1587,7 @@ static inline int jbd2_space_needed(journal_t *journal)
		static inline unsigned long jbd2_log_space_left(journal_t *journal)
		{
		/* Allow for rounding errors */
		unsigned long free = journal->j_free - 32;
		long free = journal->j_free - 32;

		if (journal->j_committing_transaction) {
		unsigned long committing = atomic_read(&journal->
		@@ -1596,7 +1596,7 @@ static inline unsigned long jbd2_log_space_left(journal_t *journal)
		/* Transaction + control blocks */
		free -= committing + (committing >> JBD2_CONTROL_BLOCKS_SHIFT);
		}
		return free;
		return max_t(long, free, 0);
		}

		/*