linux-kernel - [PATCH v2] smp: Fix a potential usage of stale nr

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Date:   Sat, 18 Jul 2020 14:11:44 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     peterz@...radead.org, tglx@...utronix.de, mingo@...nel.org,
        bigeasy@...utronix.de, namit@...are.com
Cc:     linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2] smp: Fix a potential usage of stale nr_cpus

When the cmdline of "nr_cpus" is not valid, the @nr_cpu_ids is assigned
a stale value. The nr_cpus is only valid when get_option() return 1. So
check the return value to prevent this.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
changelog in v2:
 1) Rework the commit log.
 2) Rework the return value check.


 kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index a5a66fc28f4e..0bc260158047 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -772,8 +772,8 @@ static int __init nrcpus(char *str)
 {
 	int nr_cpus;
 
-	get_option(&str, &nr_cpus);
-	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
+	if ((get_option(&str, &nr_cpus) == 1) &&
+	    nr_cpus > 0 && nr_cpus < nr_cpu_ids)
 		nr_cpu_ids = nr_cpus;
 
 	return 0;
-- 
2.11.0