[PATCH 4.9 141/271] kdb: do a sanity check on the cpu in kdb_per_cpu()

[Greg Kroah-Hartman]

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

[ Upstream commit b586627e10f57ee3aa8f0cfab0d6f7dc4ae63760 ]

The "whichcpu" comes from argv[3].  The cpu_online() macro looks up the
cpu in a bitmap of online cpus, but if the value is too high then it
could read beyond the end of the bitmap and possibly Oops.

Fixes: 5d5314d6795f ("kdb: core for kgdb back end (1 of 2)")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/debug/kdb/kdb_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 5a58421d7e2d7..a52a6da8c3d09 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2632,7 +2632,7 @@ static int kdb_per_cpu(int argc, const char **argv)
 		diag = kdbgetularg(argv[3], &whichcpu);
 		if (diag)
 			return diag;
-		if (!cpu_online(whichcpu)) {
+		if (whichcpu >= nr_cpu_ids || !cpu_online(whichcpu)) {
 			kdb_printf("cpu %ld is not online\n", whichcpu);
 			return KDB_BADCPUNUM;
 		}
-- 
2.20.1