linux-kernel - [PATCH AUTOSEL 4.9 094/251] xen, cpu_hotplug: Prevent an out of bounds access

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Message-Id: <20200116173641.22137-54-sashal@kernel.org>
Date:   Thu, 16 Jan 2020 12:34:03 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Sasha Levin <sashal@...nel.org>, xen-devel@...ts.xenproject.org
Subject: [PATCH AUTOSEL 4.9 094/251] xen, cpu_hotplug: Prevent an out of bounds access

From: Dan Carpenter <dan.carpenter@...cle.com>

[ Upstream commit 201676095dda7e5b31a5e1d116d10fc22985075e ]

The "cpu" variable comes from the sscanf() so Smatch marks it as
untrusted data.  We can't pass a higher value than "nr_cpu_ids" to
cpu_possible() or it results in an out of bounds access.

Fixes: d68d82afd4c8 ("xen: implement CPU hotplugging")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Reviewed-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/xen/cpu_hotplug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index f4e59c445964..17054d695411 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -53,7 +53,7 @@ static int vcpu_online(unsigned int cpu)
 }
 static void vcpu_hotplug(unsigned int cpu)
 {
-	if (!cpu_possible(cpu))
+	if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
 		return;
 
 	switch (vcpu_online(cpu)) {
-- 
2.20.1