selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c.

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;

Now, the verifier does not complain without the boundary check.
Let's remove the checks.

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>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240821013425.49316-1-kuniyu@amazon.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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 44ee0d037f955cefdc66266afbb8742d94e57387..eb5cca1fce16e7f7b0280a3858408f13742cf171 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
@@ -486,17 +486,10 @@ static int tcp_validate_cookie(struct tcp_syncookie *ctx)
                goto err;
 
        mssind = (cookie & (3 << 6)) >> 6;
-       if (ctx->ipv4) {
-               if (mssind > ARRAY_SIZE(msstab4))
-                       goto err;
-
+       if (ctx->ipv4)
                ctx->attrs.mss = msstab4[mssind];
-       } else {
-               if (mssind > ARRAY_SIZE(msstab6))
-                       goto err;
-
+       else
                ctx->attrs.mss = msstab6[mssind];
-       }
 
        ctx->attrs.snd_wscale = cookie & BPF_SYNCOOKIE_WSCALE_MASK;
        ctx->attrs.rcv_wscale = ctx->attrs.snd_wscale;