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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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