linux-kernel - [PATCH] psi: fix integer overflow on unsigned int multiply on 32 bit systems

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Date:   Mon,  6 Sep 2021 17:55:24 +0530
From:   Ravi Singh <ravi.singh1@...sung.com>
To:     hannes@...xchg.org, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Cc:     a.sahrawat@...sung.com, v.narang@...sung.com,
        vishal.goel@...sung.com, Ravi Singh <ravi.singh1@...sung.com>
Subject: [PATCH] psi: fix integer overflow on unsigned int multiply on 32
 bit systems

psi accepts window sizes upto WINDOW_MAX_US(10000000). In the case
where window_us is larger than 4294967, the result of an
multiplication overflows an unsigned int/long(4 bytes on 32 bit
system).

For example, this can happen when the window_us is 5000000 so 5000000
* 1000 (NSEC_PER_USEC) will result in 5000000000 which is greater than
UINT_MAX(4294967295). Due to this overflow, 705032704 is stored in
t->win.size instead of 5000000000. Now psi will be monitoring the
window size of 705 msecs instead of 5 secs as expected by user.

Fix this by type casting the first term of the mutiply to a u64.

Issue doesnot occur on 64 bit systems because NSEC_PER_USEC is of type
long which is 8 bytes on 64 bit systems.

Signed-off-by: Ravi Singh <ravi.singh1@...sung.com>
Signed-off-by: Vishal Goel <vishal.goel@...sung.com>
---
 kernel/sched/psi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 1652f2bb5..a2cc33dc2 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1145,7 +1145,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
 	t->group = group;
 	t->state = state;
 	t->threshold = threshold_us * NSEC_PER_USEC;
-	t->win.size = window_us * NSEC_PER_USEC;
+	t->win.size = (u64)window_us * NSEC_PER_USEC;
 	window_reset(&t->win, 0, 0, 0);

 	t->event = 0;
-- 
2.17.1