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    Subject[PATCH 3/3] blkio-throttle: Fix possible multiplication overflow in iops calculations
    Date
    o User can specify max iops value of 32bit (UINT_MAX), through cgroup
    interface. If a user has specified say 4294967294 (UNIT_MAX - 2), then
    on 32bit platform, following multiplication can overflow.

    io_allowed = (tg->iops[rw] * jiffy_elapsed_rnd)

    o Explicitly cast the multiplication to 64bit and then perform division and
    then check whether result is still great then UNINT_MAX.

    Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
    ---
    block/blk-throttle.c | 16 +++++++++++++++-
    1 files changed, 15 insertions(+), 1 deletions(-)

    diff --git a/block/blk-throttle.c b/block/blk-throttle.c
    index c1bc1b6..56ad453 100644
    --- a/block/blk-throttle.c
    +++ b/block/blk-throttle.c
    @@ -430,6 +430,7 @@ static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
    bool rw = bio_data_dir(bio);
    unsigned int io_allowed;
    unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
    + u64 tmp;

    jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];

    @@ -439,7 +440,20 @@ static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,

    jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);

    - io_allowed = (tg->iops[rw] * jiffy_elapsed_rnd) / HZ;
    + /*
    + * jiffy_elapsed_rnd should not be a big value as minimum iops can be
    + * 1 then at max jiffy elapsed should be equivalent of 1 second as we
    + * will allow dispatch after 1 second and after that slice should
    + * have been trimmed.
    + */
    +
    + tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
    + do_div(tmp, HZ);
    +
    + if (tmp > UINT_MAX)
    + io_allowed = UINT_MAX;
    + else
    + io_allowed = tmp;

    if (tg->io_disp[rw] + 1 <= io_allowed) {
    if (wait)
    --
    1.7.2.3


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