Re: [PATCH v7 bpf-next 6/6] selftest: bpf: Test bpf_sk_assign_tcp_reqsk().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Martin KaFai Lau <martin.lau@linux.dev>
Date: Wed, 20 Dec 2023 22:35:26 -0800
> On 12/20/23 5:28 PM, Kuniyuki Iwashima wrote:
> > +static int tcp_validate_header(struct tcp_syncookie *ctx)
> > +{
> > +	s64 csum;
> > +
> > +	if (tcp_reload_headers(ctx))
> > +		goto err;
> > +
> > +	csum = bpf_csum_diff(0, 0, (void *)ctx->tcp, ctx->tcp->doff * 4, 0);
> > +	if (csum < 0)
> > +		goto err;
> > +
> > +	if (ctx->ipv4) {
> > +		/* check tcp_v4_csum(csum) is 0 if not on lo. */
> > +
> > +		csum = bpf_csum_diff(0, 0, (void *)ctx->ipv4, ctx->ipv4->ihl * 4, 0);
> > +		if (csum < 0)
> > +			goto err;
> > +
> > +		if (csum_fold(csum) != 0)
> > +			goto err;
> > +	} else if (ctx->ipv6) {
> > +		/* check tcp_v6_csum(csum) is 0 if not on lo. */
> > +	}
> > +
> > +	return 0;
> > +err:
> > +	return -1;
> > +}
> > +
> > +static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx)
> > +{
> > +	char opcode, opsize;
> > +
> > +	if (ctx->ptr + 1 > ctx->data_end)
> > +		goto stop;
> > +
> > +	opcode = *ctx->ptr++;
> > +
> > +	if (opcode == TCPOPT_EOL)
> > +		goto stop;
> > +
> > +	if (opcode == TCPOPT_NOP)
> > +		goto next;
> > +
> > +	if (ctx->ptr + 1 > ctx->data_end)
> > +		goto stop;
> > +
> > +	opsize = *ctx->ptr++;
> > +
> > +	if (opsize < 2)
> > +		goto stop;
> > +
> > +	switch (opcode) {
> > +	case TCPOPT_MSS:
> > +		if (opsize == TCPOLEN_MSS && ctx->tcp->syn &&
> > +		    ctx->ptr + (TCPOLEN_MSS - 2) < ctx->data_end)
> > +			ctx->attrs.mss = get_unaligned_be16(ctx->ptr);
> > +		break;
> > +	case TCPOPT_WINDOW:
> > +		if (opsize == TCPOLEN_WINDOW && ctx->tcp->syn &&
> > +		    ctx->ptr + (TCPOLEN_WINDOW - 2) < ctx->data_end) {
> > +			ctx->attrs.wscale_ok = 1;
> > +			ctx->attrs.snd_wscale = *ctx->ptr;
> > +		}
> > +		break;
> > +	case TCPOPT_TIMESTAMP:
> > +		if (opsize == TCPOLEN_TIMESTAMP &&
> > +		    ctx->ptr + (TCPOLEN_TIMESTAMP - 2) < ctx->data_end) {
> > +			ctx->attrs.rcv_tsval = get_unaligned_be32(ctx->ptr);
> > +			ctx->attrs.rcv_tsecr = get_unaligned_be32(ctx->ptr + 4);
> > +
> > +			if (ctx->tcp->syn && ctx->attrs.rcv_tsecr)
> > +				ctx->attrs.tstamp_ok = 0;
> > +			else
> > +				ctx->attrs.tstamp_ok = 1;
> > +		}
> > +		break;
> > +	case TCPOPT_SACK_PERM:
> > +		if (opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn &&
> > +		    ctx->ptr + (TCPOLEN_SACK_PERM - 2) < ctx->data_end)
> > +			ctx->attrs.sack_ok = 1;
> > +		break;
> > +	}
> > +
> > +	ctx->ptr += opsize - 2;
> > +next:
> > +	return 0;
> > +stop:
> > +	return 1;
> > +}
> > +
> > +static void tcp_parse_options(struct tcp_syncookie *ctx)
> > +{
> > +	ctx->ptr = (char *)(ctx->tcp + 1);
> > +
> > +	bpf_loop(40, tcp_parse_option, ctx, 0);
> > +}
> > +
> > +static int tcp_validate_sysctl(struct tcp_syncookie *ctx)
> > +{
> > +	if ((ctx->ipv4 && ctx->attrs.mss != MSS_LOCAL_IPV4) ||
> > +	    (ctx->ipv6 && ctx->attrs.mss != MSS_LOCAL_IPV6))
> > +		goto err;
> > +
> > +	if (!ctx->attrs.wscale_ok || ctx->attrs.snd_wscale != 7)
> > +		goto err;
> > +
> > +	if (!ctx->attrs.tstamp_ok)
> 
> The bpf-ci reported error in cpuv4. The email from bot+bpf-ci@kernel.org has the 
> link.

I like the mail from the bot, it's useful, but it seems that
it's sent to the patch author only when the CI passes ?

But yeah, I found the failed test.
https://github.com/kernel-patches/bpf/actions/runs/7284164398/job/19849657597


> 
> I tried the following:
> 
> 	if (!ctx->attrs.tstamp_ok) {
> 		bpf_printk("ctx->attrs.tstamp_ok %u",
> 			ctx->attrs.tstamp_ok);
> 		goto err;
> 	}
> 
> 
> The above prints tstamp_ok as 1 while there is a "if (!ctx->attrs.tstamp_ok)" 
> test before it.
> 
> Yonghong and I debugged it quite a bit. verifier concluded the 
> ctx->attrs.tstamp_ok is 0. We knew some red herring like cpuv4 has fewer 
> register spilling but not able to root cause it yet.
> 
> In the mean time, there are existing selftests parsing the tcp header. For 
> example, the test_parse_tcp_hdr_opt[_dynptr].c. Not as complete as your 
> tcp_parse_option() but should be pretty close. It does not use bpf_loop. It uses 
> a bounded loop + a subprog (the parse_hdr_opt in the selftests) instead. You can 
> consider a similar construct to see if it works around the cpuv4 CI issue for 
> the time being.

Sure, I'll install the latest clang/llvm and check if the test
passes without bpf_loop().

Thanks!