diff options
| author | Stephen Hemminger <stephen@networkplumber.org> | 2026-04-17 20:19:43 -0700 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-04-27 17:30:28 -0700 |
| commit | 51e94e1e2fef351c74d69eb53666df808d26af95 (patch) | |
| tree | 16817f4d046eeeca8ac4cec98e00ffda43e8273b /net | |
| parent | 01801c359a74737b9b1aa28568b60374d857241a (diff) | |
net/sched: netem: fix slot delay calculation overflow
get_slot_next() computes a random delay between min_delay and
max_delay using:
get_random_u32() * (max_delay - min_delay) >> 32
This overflows signed 64-bit arithmetic when the delay range exceeds
approximately 2.1 seconds (2^31 nanoseconds), producing a negative
result that effectively disables slot-based pacing. This is a
realistic configuration for WAN emulation (e.g., slot 1s 5s).
Use mul_u64_u32_shr() which handles the widening multiply without
overflow.
Fixes: 0a9fe5c375b5 ("netem: slotting with non-uniform distribution")
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260418032027.900913-6-stephen@networkplumber.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/sched/sch_netem.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 640b51be807a..475c14b3dbdb 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -659,9 +659,8 @@ static void get_slot_next(struct netem_sched_data *q, u64 now) if (!q->slot_dist) next_delay = q->slot_config.min_delay + - (get_random_u32() * - (q->slot_config.max_delay - - q->slot_config.min_delay) >> 32); + mul_u64_u32_shr(q->slot_config.max_delay - q->slot_config.min_delay, + get_random_u32(), 32); else next_delay = tabledist(q->slot_config.dist_delay, (s32)(q->slot_config.dist_jitter), |