[PATCH v1 bpf-next] selftest: bpf: Correct mssind comparison in test_tcp_custom_syncookie.c.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

Smatch reported a possible off-by-one in tcp_validate_cookie().

However, it's false positive because the possible range of mssind is
limited from 0 to 3 by the preceding calculation.

  mssind = (cookie & (3 << 6)) >> 6;

There's no real issue, but let's make Smatch happy to suppress the same
reports.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/bpf/6ae12487-d3f1-488b-9514-af0dac96608f@stanley.mountain/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
index 44ee0d037f95..36b842133033 100644
--- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
@@ -487,12 +487,12 @@ static int tcp_validate_cookie(struct tcp_syncookie *ctx)
 
 	mssind = (cookie & (3 << 6)) >> 6;
 	if (ctx->ipv4) {
-		if (mssind > ARRAY_SIZE(msstab4))
+		if (mssind >= ARRAY_SIZE(msstab4))
 			goto err;
 
 		ctx->attrs.mss = msstab4[mssind];
 	} else {
-		if (mssind > ARRAY_SIZE(msstab6))
+		if (mssind >= ARRAY_SIZE(msstab6))
 			goto err;
 
 		ctx->attrs.mss = msstab6[mssind];
-- 
2.30.2