Re: [PATCH bpf-next 09/10] bpf: Add a helper to issue timestamp cookies in XDP

[Maxim Mikityanskiy <maximmi@nvidia.com>]

On 2021-10-19 19:45, Eric Dumazet wrote:
> 
> 
> On 10/19/21 7:46 AM, Maxim Mikityanskiy wrote:
>> The new helper bpf_tcp_raw_gen_tscookie allows an XDP program to
>> generate timestamp cookies (to be used together with SYN cookies) which
>> encode different options set by the client in the SYN packet: SACK
>> support, ECN support, window scale. These options are encoded in lower
>> bits of the timestamp, which will be returned by the client in a
>> subsequent ACK packet. The format is the same used by synproxy.
>>
>> Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
>> Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
>> ---
>>   include/net/tcp.h              |  1 +
>>   include/uapi/linux/bpf.h       | 27 +++++++++++++++
>>   net/core/filter.c              | 38 +++++++++++++++++++++
>>   net/ipv4/syncookies.c          | 60 ++++++++++++++++++++++++++++++++++
>>   tools/include/uapi/linux/bpf.h | 27 +++++++++++++++
>>   5 files changed, 153 insertions(+)
>>
>> diff --git a/include/net/tcp.h b/include/net/tcp.h
>> index 1cc96a225848..651820bef6a2 100644
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -564,6 +564,7 @@ u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
>>   			      u16 *mssp);
>>   __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
>>   u64 cookie_init_timestamp(struct request_sock *req, u64 now);
>> +bool cookie_init_timestamp_raw(struct tcphdr *th, __be32 *tsval, __be32 *tsecr);
>>   bool cookie_timestamp_decode(const struct net *net,
>>   			     struct tcp_options_received *opt);
>>   bool cookie_ecn_ok(const struct tcp_options_received *opt,
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index e32f72077250..791790b41874 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -5053,6 +5053,32 @@ union bpf_attr {
>>    *
>>    *		**-EPROTONOSUPPORT** if the IP version is not 4 or 6 (or 6, but
>>    *		CONFIG_IPV6 is disabled).
>> + *
>> + * int bpf_tcp_raw_gen_tscookie(struct tcphdr *th, u32 th_len, __be32 *tsopt, u32 tsopt_len)
>> + *	Description
>> + *		Try to generate a timestamp cookie which encodes some of the
>> + *		flags sent by the client in the SYN packet: SACK support, ECN
>> + *		support, window scale. To be used with SYN cookies.
>> + *
>> + *		*th* points to the start of the TCP header of the client's SYN
>> + *		packet, while *th_len* contains the length of the TCP header (at
>> + *		least **sizeof**\ (**struct tcphdr**)).
>> + *
>> + *		*tsopt* points to the output location where to put the resulting
>> + *		timestamp values: tsval and tsecr, in the format of the TCP
>> + *		timestamp option.
>> + *
>> + *	Return
>> + *		On success, 0.
>> + *
>> + *		On failure, the returned value is one of the following:
>> + *
>> + *		**-EINVAL** if the input arguments are invalid.
>> + *
>> + *		**-ENOENT** if the TCP header doesn't have the timestamp option.
>> + *
>> + *		**-EOPNOTSUPP** if the kernel configuration does not enable SYN
>> + *		cookies (CONFIG_SYN_COOKIES is off).
>>    */
>>   #define __BPF_FUNC_MAPPER(FN)		\
>>   	FN(unspec),			\
>> @@ -5238,6 +5264,7 @@ union bpf_attr {
>>   	FN(ct_release),			\
>>   	FN(tcp_raw_gen_syncookie),	\
>>   	FN(tcp_raw_check_syncookie),	\
>> +	FN(tcp_raw_gen_tscookie),	\
>>   	/* */
>>   
>>   /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 5f03d4a282a0..73fe20ef7442 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -7403,6 +7403,42 @@ static const struct bpf_func_proto bpf_tcp_raw_check_syncookie_proto = {
>>   	.arg4_type	= ARG_CONST_SIZE,
>>   };
>>   
>> +BPF_CALL_4(bpf_tcp_raw_gen_tscookie, struct tcphdr *, th, u32, th_len,
>> +	   __be32 *, tsopt, u32, tsopt_len)
>> +{
>> +	int err;
>> +
>> +#ifdef CONFIG_SYN_COOKIES
>> +	if (tsopt_len != sizeof(u64)) {
>> +		err = -EINVAL;
>> +		goto err_out;
>> +	}
>> +
>> +	if (!cookie_init_timestamp_raw(th, &tsopt[0], &tsopt[1])) {
>> +		err = -ENOENT;
>> +		goto err_out;
>> +	}
>> +
>> +	return 0;
>> +err_out:
>> +#else
>> +	err = -EOPNOTSUPP;
>> +#endif
>> +	memset(tsopt, 0, tsopt_len);
>> +	return err;
>> +}
>> +
>> +static const struct bpf_func_proto bpf_tcp_raw_gen_tscookie_proto = {
>> +	.func		= bpf_tcp_raw_gen_tscookie,
>> +	.gpl_only	= false,
>> +	.pkt_access	= true,
>> +	.ret_type	= RET_INTEGER,
>> +	.arg1_type	= ARG_PTR_TO_MEM,
>> +	.arg2_type	= ARG_CONST_SIZE,
>> +	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,
>> +	.arg4_type	= ARG_CONST_SIZE,
>> +};
>> +
>>   #endif /* CONFIG_INET */
>>   
>>   bool bpf_helper_changes_pkt_data(void *func)
>> @@ -7825,6 +7861,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>>   		return &bpf_tcp_raw_gen_syncookie_proto;
>>   	case BPF_FUNC_tcp_raw_check_syncookie:
>>   		return &bpf_tcp_raw_check_syncookie_proto;
>> +	case BPF_FUNC_tcp_raw_gen_tscookie:
>> +		return &bpf_tcp_raw_gen_tscookie_proto;
>>   #endif
>>   	default:
>>   		return bpf_sk_base_func_proto(func_id);
>> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
>> index 8696dc343ad2..4dd2c7a096eb 100644
>> --- a/net/ipv4/syncookies.c
>> +++ b/net/ipv4/syncookies.c
>> @@ -85,6 +85,66 @@ u64 cookie_init_timestamp(struct request_sock *req, u64 now)
>>   	return (u64)ts * (NSEC_PER_SEC / TCP_TS_HZ);
>>   }
>>   
>> +bool cookie_init_timestamp_raw(struct tcphdr *th, __be32 *tsval, __be32 *tsecr)
>> +{
>> +	int length = (th->doff * 4) - sizeof(*th);
>> +	u8 wscale = TS_OPT_WSCALE_MASK;
>> +	bool option_timestamp = false;
>> +	bool option_sack = false;
>> +	u32 cookie;
>> +	u8 *ptr;
>> +
>> +	ptr = (u8 *)(th + 1);
>> +
>> +	while (length > 0) {
>> +		u8 opcode = *ptr++;
>> +		u8 opsize;
>> +
>> +		if (opcode == TCPOPT_EOL)
>> +			break;
>> +		if (opcode == TCPOPT_NOP) {
>> +			length--;
>> +			continue;
>> +		}
>> +
>> +		if (length < 2)
>> +			break;
>> +		opsize = *ptr++;
>> +		if (opsize < 2)
>> +			break;
>> +		if (opsize > length)
>> +			break;
>> +
>> +		switch (opcode) {
>> +		case TCPOPT_WINDOW:
> 
> You must check osize.
> 
>> +			wscale = min_t(u8, *ptr, TCP_MAX_WSCALE);
>> +			break;
>> +		case TCPOPT_TIMESTAMP:
> 
> You must check opsize.

Ack.

>> +			option_timestamp = true;
>> +			/* Client's tsval becomes our tsecr. */
>> +			*tsecr = cpu_to_be32(get_unaligned_be32(ptr));
> 
> Please avoid useless ntohl/htonl dance (even if compiler probably optimizes this)
> No need to obfuscate :)

No obfuscation intended - I thought I was clearer this way. I can change it.

Thanks for reviewing!

> 
> 			*tsecr = get_unaligned((__be32 *)ptr);
> 
>> +			break;
>> +		case TCPOPT_SACK_PERM:
>> +			option_sack = true;
>> +			break;
>> +		}
>> +
>> +		ptr += opsize - 2;
>> +		length -= opsize;
>> +	}
>> +
>> +	if (!option_timestamp)
>> +		return false;
>> +
>> +	cookie = tcp_time_stamp_raw() & ~TSMASK;
>> +	cookie |= wscale & TS_OPT_WSCALE_MASK;
>> +	if (option_sack)
>> +		cookie |= TS_OPT_SACK;
>> +	if (th->ece && th->cwr)
>> +		cookie |= TS_OPT_ECN;
>> +	*tsval = cpu_to_be32(cookie);
>> +	return true;
>> +}
>>   
>>   static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
>>   				   __be16 dport, __u32 sseq, __u32 data)
>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>> index e32f72077250..791790b41874 100644
>> --- a/tools/include/uapi/linux/bpf.h
>> +++ b/tools/include/uapi/linux/bpf.h
>> @@ -5053,6 +5053,32 @@ union bpf_attr {
>>    *
>>    *		**-EPROTONOSUPPORT** if the IP version is not 4 or 6 (or 6, but
>>    *		CONFIG_IPV6 is disabled).
>> + *
>> + * int bpf_tcp_raw_gen_tscookie(struct tcphdr *th, u32 th_len, __be32 *tsopt, u32 tsopt_len)
>> + *	Description
>> + *		Try to generate a timestamp cookie which encodes some of the
>> + *		flags sent by the client in the SYN packet: SACK support, ECN
>> + *		support, window scale. To be used with SYN cookies.
>> + *
>> + *		*th* points to the start of the TCP header of the client's SYN
>> + *		packet, while *th_len* contains the length of the TCP header (at
>> + *		least **sizeof**\ (**struct tcphdr**)).
>> + *
>> + *		*tsopt* points to the output location where to put the resulting
>> + *		timestamp values: tsval and tsecr, in the format of the TCP
>> + *		timestamp option.
>> + *
>> + *	Return
>> + *		On success, 0.
>> + *
>> + *		On failure, the returned value is one of the following:
>> + *
>> + *		**-EINVAL** if the input arguments are invalid.
>> + *
>> + *		**-ENOENT** if the TCP header doesn't have the timestamp option.
>> + *
>> + *		**-EOPNOTSUPP** if the kernel configuration does not enable SYN
>> + *		cookies (CONFIG_SYN_COOKIES is off).
>>    */
>>   #define __BPF_FUNC_MAPPER(FN)		\
>>   	FN(unspec),			\
>> @@ -5238,6 +5264,7 @@ union bpf_attr {
>>   	FN(ct_release),			\
>>   	FN(tcp_raw_gen_syncookie),	\
>>   	FN(tcp_raw_check_syncookie),	\
>> +	FN(tcp_raw_gen_tscookie),	\
>>   	/* */
>>   
>>   /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>>