[PATCH bpf] samples/bpf: Fix Segmentation fault for xdp_redirect command

[Wang Hai <wanghai38@huawei.com>]

A Segmentation fault error is caused when the following command
is executed.

$ sudo ./samples/bpf/xdp_redirect lo
Segmentation fault

This command is missing a device <IFNAME|IFINDEX> as an argument, resulting
in out-of-bounds access from argv.

If the number of devices for the xdp_redirect parameter is not 2,
we should report an error and exit.

Fixes: 24251c264798 ("samples/bpf: add option for native and skb mode for redirect apps")
Signed-off-by: Wang Hai <wanghai38@huawei.com>
---
 samples/bpf/xdp_redirect_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/xdp_redirect_user.c b/samples/bpf/xdp_redirect_user.c
index c903f1ccc15e..93854e135134 100644
--- a/samples/bpf/xdp_redirect_user.c
+++ b/samples/bpf/xdp_redirect_user.c
@@ -130,7 +130,7 @@ int main(int argc, char **argv)
 	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))
 		xdp_flags |= XDP_FLAGS_DRV_MODE;
 
-	if (optind == argc) {
+	if (optind + 2 != argc) {
 		printf("usage: %s <IFNAME|IFINDEX>_IN <IFNAME|IFINDEX>_OUT\n", argv[0]);
 		return 1;
 	}
-- 
2.17.1