[bug report] selftest: bpf: Test bpf_sk_assign_tcp_reqsk().

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Kuniyuki Iwashima,

Commit a74712241b46 ("selftest: bpf: Test
bpf_sk_assign_tcp_reqsk().") from Jan 15, 2024 (linux-next), leads to
the following Smatch static checker warning:

	tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c:493 tcp_validate_cookie()
	warn: off by one 'mssind' == ARRAY_SIZE()?

./tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
    462 static int tcp_validate_cookie(struct tcp_syncookie *ctx)
    463 {
    464         u32 cookie = bpf_ntohl(ctx->tcp->ack_seq) - 1;
    465         u32 seq = bpf_ntohl(ctx->tcp->seq) - 1;
    466         u64 first = 0, second;
    467         int mssind;
    468         u32 hash;
    469 
    470         if (ctx->ipv4)
    471                 first = (u64)ctx->ipv4->saddr << 32 | ctx->ipv4->daddr;
    472         else if (ctx->ipv6)
    473                 first = (u64)ctx->ipv6->saddr.in6_u.u6_addr8[0] << 32 |
    474                         ctx->ipv6->daddr.in6_u.u6_addr32[0];
    475 
    476         second = (u64)seq << 32 | ctx->tcp->source << 16 | ctx->tcp->dest;
    477         hash = siphash_2u64(first, second, &test_key_siphash);
    478 
    479         if (ctx->attrs.tstamp_ok)
    480                 hash -= ctx->attrs.rcv_tsecr & COOKIE_MASK;
    481         else
    482                 hash &= ~COOKIE_MASK;
    483 
    484         hash -= cookie & ~COOKIE_MASK;
    485         if (hash)
    486                 goto err;
    487 
    488         mssind = (cookie & (3 << 6)) >> 6;
    489         if (ctx->ipv4) {
    490                 if (mssind > ARRAY_SIZE(msstab4))
                                   ^
Should be >= instead of >.

    491                         goto err;
    492 
--> 493                 ctx->attrs.mss = msstab4[mssind];
    494         } else {
    495                 if (mssind > ARRAY_SIZE(msstab6))
    496                         goto err;
    497 
    498                 ctx->attrs.mss = msstab6[mssind];
    499         }
    500 
    501         ctx->attrs.snd_wscale = cookie & BPF_SYNCOOKIE_WSCALE_MASK;
    502         ctx->attrs.rcv_wscale = ctx->attrs.snd_wscale;
    503         ctx->attrs.wscale_ok = ctx->attrs.snd_wscale == BPF_SYNCOOKIE_WSCALE_MASK;
    504         ctx->attrs.sack_ok = cookie & BPF_SYNCOOKIE_SACK;
    505         ctx->attrs.ecn_ok = cookie & BPF_SYNCOOKIE_ECN;
    506 
    507         return 0;
    508 err:
    509         return -1;
    510 }

regards,
dan carpenter