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    Subject[PATCH 5.4 53/92] jbd2: Fix possible overflow in jbd2_log_space_left()
    Date
    From: Jan Kara <jack@suse.cz>

    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>

    ---
    include/linux/jbd2.h | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/include/linux/jbd2.h
    +++ b/include/linux/jbd2.h
    @@ -1582,7 +1582,7 @@ static inline int jbd2_space_needed(jour
    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->
    @@ -1591,7 +1591,7 @@ static inline unsigned long jbd2_log_spa
    /* Transaction + control blocks */
    free -= committing + (committing >> JBD2_CONTROL_BLOCKS_SHIFT);
    }
    - return free;
    + return max_t(long, free, 0);
    }

    /*

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