linux-hardening - [PATCH] sched/psi: Bounds-check state iterator against NR_PSI

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Date:   Fri, 20 May 2022 09:58:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] sched/psi: Bounds-check state iterator against NR_PSI_STATES

GCC 12 cannot tell that "t" will be bounded by NR_PSI_STATES, which could
lead to walking off the end of the tasks array, which is NR_PSI_STATES in
size. Explicitly bounds-check "t" as part of the loop.

In file included from ../kernel/sched/build_utility.c:97:
../kernel/sched/psi.c: In function 'psi_group_change':
../kernel/sched/psi.c:730:38: warning: array subscript 32 is above array bounds of 'unsigned int[5]' [-Warray-bounds]
  730 |                         groupc->tasks[t]++;
      |                         ~~~~~~~~~~~~~^~~
In file included from ../include/linux/psi.h:6,
                 from ../kernel/sched/build_utility.c:36:
../include/linux/psi_types.h:84:22: note: while referencing 'tasks'
   84 |         unsigned int tasks[NR_PSI_TASK_COUNTS];
      |                      ^~~~~
../kernel/sched/psi.c:730:38: warning: array subscript 32 is above array bounds of 'unsigned int[5]' [-Warray-bounds]
  730 |                         groupc->tasks[t]++;
      |                         ~~~~~~~~~~~~~^~~
../include/linux/psi_types.h:84:22: note: while referencing 'tasks'
   84 |         unsigned int tasks[NR_PSI_TASK_COUNTS];
      |                      ^~~~~

Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Valentin Schneider <vschneid@...hat.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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 a337f3e35997..827f16a79936 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -725,7 +725,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
 		}
 	}
 
-	for (t = 0; set; set &= ~(1 << t), t++)
+	for (t = 0; set && t < ARRAY_SIZE(groupc->tasks); set &= ~(1 << t), t++)
 		if (set & (1 << t))
 			groupc->tasks[t]++;
 
-- 
2.32.0