[PATCH 2/2] sched/psi: Fix overflow in trigger time conversion on 32-bit

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>

threshold_us and window_us are u32, while NSEC_PER_USEC is 1000L. On
32-bit architectures, multiplication by NSEC_PER_USEC is evaluated
using 32-bit unsigned arithmetic and can wrap before the result is
assigned to the u64 trigger fields.

For a valid 4,000,000 us threshold and 6,000,000 us window, the
threshold is stored as 4,000,000,000 ns, while the window wraps to
1,705,032,704 ns. The stored window is therefore shorter than the
threshold, so the trigger no longer monitors the requested 4-second
threshold over a 6-second window.

Cast both values to u64 before the multiplication so that the
conversion to nanoseconds is performed using 64-bit arithmetic.

Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Signed-off-by: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>
---
 kernel/sched/psi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 8e4df8b17c25..f0a5976f49dc 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1391,8 +1391,8 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
 
 	t->group = group;
 	t->state = state;
-	t->threshold = threshold_us * NSEC_PER_USEC;
-	t->win.size = window_us * NSEC_PER_USEC;
+	t->threshold = (u64)threshold_us * NSEC_PER_USEC;
+	t->win.size = (u64)window_us * NSEC_PER_USEC;
 	window_reset(&t->win, sched_clock(),
 			group->total[PSI_POLL][t->state], 0);
 
-- 
2.43.0