[PATCH 3.16 109/129] xen, cpu_hotplug: Prevent an out of bounds access

[Ben Hutchings]

3.16.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit 201676095dda7e5b31a5e1d116d10fc22985075e upstream.

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@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/xen/cpu_hotplug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -47,7 +47,7 @@ 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)) {