This code has an integer overflow or sign extension bug which was caught
by gcc-13:

  kernel/sched/debug.c:341:57: error: integer overflow in expression of
  type 'long int' results in '-100663296' [-Werror=overflow]
    341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */

The result is that "fair_server_period_max" is set to 0xfffffffffa000000
(585 years) instead of instead of 0xfa000000 (4 seconds) that was
intended.

Fix this by changing the type to shift from (1 << 22) to (1UL << 22).

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/all/CA+G9fYtE2GAbeqU+AOCffgo2oH0RTJUxU+=Pi3cFn4di_KgBAQ@mail.gmail.com/
Fixes: d741f297bcea ("sched/fair: Fair server interface")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 0148bc65d39c..845b79238398 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -338,7 +338,7 @@ enum dl_param {
 	DL_PERIOD,
 };
 
-static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
+static unsigned long fair_server_period_max = (1UL << 22) * NSEC_PER_USEC; /* ~4 seconds */
 static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
 
 static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
-- 
2.43.0

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     4ae0c2b91110dab6f4291c2c7f99dde60ecc97d8
Gitweb:        https://git.kernel.org/tip/4ae0c2b91110dab6f4291c2c7f99dde60ecc97d8
Author:        Dan Carpenter <dan.carpenter@linaro.org>
AuthorDate:    Thu, 01 Aug 2024 10:44:03 -05:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Aug 2024 12:44:16 +02:00

sched/debug: Fix fair_server_period_max value

This code has an integer overflow or sign extension bug which was caught
by gcc-13:

  kernel/sched/debug.c:341:57: error: integer overflow in expression of
  type 'long int' results in '-100663296' [-Werror=overflow]
    341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */

The result is that "fair_server_period_max" is set to 0xfffffffffa000000
(585 years) instead of instead of 0xfa000000 (4 seconds) that was
intended.

Fix this by changing the type to shift from (1 << 22) to (1UL << 22).

Closes: https://lore.kernel.org/all/CA+G9fYtE2GAbeqU+AOCffgo2oH0RTJUxU+=Pi3cFn4di_KgBAQ@mail.gmail.com/
Fixes: d741f297bcea ("sched/fair: Fair server interface")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Reported-by: Arnd Bergmann <arnd@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index e75914e..831a77a 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -338,7 +338,7 @@ enum dl_param {
 	DL_PERIOD,
 };
 
-static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
+static unsigned long fair_server_period_max = (1UL << 22) * NSEC_PER_USEC; /* ~4 seconds */
 static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
 
 static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,