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net: tcp: Parse and store send MSS #4657

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Nov 8, 2017
Merged

net: tcp: Parse and store send MSS #4657

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276a61f
net: tcp: Handle storage of TCP send MSS
pfalcon Oct 31, 2017
e1be984
net: tcp: Add NET_TCP_HDR_LEN(hdr) macro for reuse
pfalcon Nov 1, 2017
9890e72
net: tcp: Add support for TCP options parsing
pfalcon Nov 2, 2017
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26 changes: 22 additions & 4 deletions subsys/net/ip/net_context.c
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@ static struct tcp_backlog_entry {
u32_t recv_max_ack;
u32_t send_seq;
u32_t send_ack;
u16_t send_mss;
struct k_delayed_work ack_timer;
} tcp_backlog[CONFIG_NET_TCP_BACKLOG_SIZE];

Expand Down Expand Up @@ -174,7 +175,8 @@ static int tcp_backlog_find(struct net_pkt *pkt, int *empty_slot)
return -EADDRNOTAVAIL;
}

static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context)
static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context,
u16_t send_mss)
{
int empty_slot = -1;
int ret;
Expand All @@ -198,6 +200,7 @@ static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context)
tcp_backlog[empty_slot].recv_max_ack = context->tcp->recv_max_ack;
tcp_backlog[empty_slot].send_seq = context->tcp->send_seq;
tcp_backlog[empty_slot].send_ack = context->tcp->send_ack;
tcp_backlog[empty_slot].send_mss = send_mss;

k_delayed_work_init(&tcp_backlog[empty_slot].ack_timer,
backlog_ack_timeout);
Expand Down Expand Up @@ -232,6 +235,7 @@ static int tcp_backlog_ack(struct net_pkt *pkt, struct net_context *context)
context->tcp->recv_max_ack = tcp_backlog[r].recv_max_ack;
context->tcp->send_seq = tcp_backlog[r].send_seq + 1;
context->tcp->send_ack = tcp_backlog[r].send_ack;
context->tcp->send_mss = tcp_backlog[r].send_mss;

k_delayed_work_cancel(&tcp_backlog[r].ack_timer);
memset(&tcp_backlog[r], 0, sizeof(struct tcp_backlog_entry));
Expand Down Expand Up @@ -1073,10 +1077,9 @@ static int tcp_hdr_len(struct net_pkt *pkt)
{
struct net_tcp_hdr hdr, *tcp_hdr;

/* "Offset": 4-bit field in high nibble, units of dwords */
tcp_hdr = net_tcp_get_hdr(pkt, &hdr);
if (tcp_hdr) {
return 4 * (tcp_hdr->offset >> 4);
return NET_TCP_HDR_LEN(tcp_hdr);
}

return 0;
Expand Down Expand Up @@ -1610,9 +1613,22 @@ NET_CONN_CB(tcp_syn_rcvd)
*/
if (NET_TCP_FLAGS(tcp_hdr) == NET_TCP_SYN) {
int r;
int opt_totlen;
struct net_tcp_options tcp_opts = {
.mss = NET_TCP_DEFAULT_MSS,
};

net_tcp_print_recv_info("SYN", pkt, tcp_hdr->src_port);

opt_totlen = NET_TCP_HDR_LEN(tcp_hdr)
- sizeof(struct net_tcp_hdr);
/* We expect MSS option to be present (opt_totlen > 0),
* so call unconditionally.
*/
if (net_tcp_parse_opts(pkt, opt_totlen, &tcp_opts) < 0) {
return NET_DROP;
}

net_tcp_change_state(tcp, NET_TCP_SYN_RCVD);

/* Set TCP seq and ack which are then stored in the backlog */
Expand All @@ -1621,7 +1637,9 @@ NET_CONN_CB(tcp_syn_rcvd)
sys_get_be32(tcp_hdr->seq) + 1;
context->tcp->recv_max_ack = context->tcp->send_seq + 1;

r = tcp_backlog_syn(pkt, context);
/* Get MSS from TCP options here*/

r = tcp_backlog_syn(pkt, context, tcp_opts.mss);
if (r < 0) {
if (r == -EADDRINUSE) {
NET_DBG("TCP connection already exists");
Expand Down
80 changes: 78 additions & 2 deletions subsys/net/ip/tcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -238,6 +238,7 @@ struct net_tcp *net_tcp_alloc(struct net_context *context)
tcp_context[i].send_seq = tcp_init_isn();
tcp_context[i].recv_max_ack = tcp_context[i].send_seq + 1u;
tcp_context[i].recv_wnd = min(NET_TCP_MAX_WIN, NET_TCP_BUF_MAX_LEN);
tcp_context[i].send_mss = NET_TCP_DEFAULT_MSS;

tcp_context[i].accept_cb = NULL;

Expand Down Expand Up @@ -599,7 +600,7 @@ u16_t net_tcp_get_recv_mss(const struct net_tcp *tcp)
static void net_tcp_set_syn_opt(struct net_tcp *tcp, u8_t *options,
u8_t *optionlen)
{
u16_t recv_mss;
u32_t recv_mss;

*optionlen = 0;

Expand All @@ -610,7 +611,8 @@ static void net_tcp_set_syn_opt(struct net_tcp *tcp, u8_t *options,
recv_mss = 0;
}

UNALIGNED_PUT(htonl((u32_t)recv_mss | NET_TCP_MSS_HEADER),
recv_mss |= (NET_TCP_MSS_OPT << 24) | (NET_TCP_MSS_SIZE << 16);
UNALIGNED_PUT(htonl(recv_mss),
(u32_t *)(options + *optionlen));

*optionlen += NET_TCP_MSS_SIZE;
Expand Down Expand Up @@ -1234,3 +1236,77 @@ struct net_buf *net_tcp_set_chksum(struct net_pkt *pkt, struct net_buf *frag)

return frag;
}

int net_tcp_parse_opts(struct net_pkt *pkt, int opt_totlen,
struct net_tcp_options *opts)
{
struct net_buf *frag = pkt->frags;
u16_t pos = net_pkt_ip_hdr_len(pkt)
+ net_pkt_ipv6_ext_len(pkt)
+ sizeof(struct net_tcp_hdr);
u8_t opt, optlen;

/* TODO: this should be done for each TCP pkt, on reception */
if (pos + opt_totlen > net_pkt_get_len(pkt)) {
NET_ERR("Truncated pkt len: %d, expected: %d",
(int)net_pkt_get_len(pkt), pos + opt_totlen);
return -EINVAL;
}

while (opt_totlen) {
frag = net_frag_read(frag, pos, &pos, sizeof(opt), &opt);
opt_totlen--;

/* https://www.iana.org/assignments/tcp-parameters/tcp-parameters.xhtml#tcp-parameters-1 */
/* "Options 0 and 1 are exactly one octet which is their
* kind field. All other options have their one octet
* kind field, followed by a one octet length field,
* followed by length-2 octets of option data."
*/
if (opt == NET_TCP_END_OPT) {
break;
} else if (opt == NET_TCP_NOP_OPT) {
continue;
}

if (!opt_totlen) {
optlen = 0;
goto error;
}

frag = net_frag_read(frag, pos, &pos, sizeof(optlen), &optlen);
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same here

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Along the discussion on IRC, I'm adding single check at the top of function.

opt_totlen--;
if (optlen < 2) {
goto error;
}

/* Subtract opt/optlen size now to avoid doing this
* repeatedly.
*/
optlen -= 2;
if (opt_totlen < optlen) {
goto error;
}

switch (opt) {
case NET_TCP_MSS_OPT:
if (optlen != 2) {
goto error;
}
frag = net_frag_read(frag, pos, &pos,
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and here

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Along the discussion on IRC, I'm adding single check at the top of function.

optlen, (u8_t *)&opts->mss);
break;
default:
frag = net_frag_skip(frag, pos, &pos, optlen);
break;
}

opt_totlen -= optlen;
}

return 0;

error:
NET_ERR("Invalid TCP opt: %d len: %d", opt, optlen);
return -EINVAL;
}
55 changes: 50 additions & 5 deletions subsys/net/ip/tcp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,15 @@ enum net_tcp_state {

#define NET_TCP_FLAGS(hdr) (hdr->flags & NET_TCP_CTL)

/* Length of TCP header, including options */
/* "offset": 4-bit field in high nibble, units of dwords */
#define NET_TCP_HDR_LEN(hdr) (4 * ((hdr)->offset >> 4))

/* RFC 1122 4.2.2.6 "If an MSS option is not received at connection
* setup, TCP MUST assume a default send MSS of 536"
*/
#define NET_TCP_DEFAULT_MSS 536

/* TCP max window size */
#define NET_TCP_MAX_WIN (4 * 1024)

Expand All @@ -80,11 +89,22 @@ enum net_tcp_state {

#define NET_TCP_MAX_OPT_SIZE 8

#define NET_TCP_MSS_HEADER 0x02040000 /* MSS option */
#define NET_TCP_WINDOW_HEADER 0x30300 /* Window scale option */

#define NET_TCP_MSS_SIZE 4 /* MSS option size */
#define NET_TCP_WINDOW_SIZE 3 /* Window scale option size */
/* TCP Option codes */
#define NET_TCP_END_OPT 0
#define NET_TCP_NOP_OPT 1
#define NET_TCP_MSS_OPT 2
#define NET_TCP_WINDOW_SCALE_OPT 3

/* TCP Option sizes */
#define NET_TCP_END_SIZE 1
#define NET_TCP_NOP_SIZE 1
#define NET_TCP_MSS_SIZE 4
#define NET_TCP_WINDOW_SCALE_SIZE 3

/** Parsed TCP option values for net_tcp_parse_opts() */
struct net_tcp_options {
u16_t mss;
};

/* Max received bytes to buffer internally */
#define NET_TCP_BUF_MAX_LEN 1280
Expand Down Expand Up @@ -148,7 +168,15 @@ struct net_tcp {
*/
struct k_sem connect_wait;

/**
* Current TCP receive window for our side
*/
u16_t recv_wnd;

/**
* Send MSS for the peer
*/
u16_t send_mss;
};

static inline bool net_tcp_is_used(struct net_tcp *tcp)
Expand Down Expand Up @@ -426,6 +454,23 @@ struct net_buf *net_tcp_set_chksum(struct net_pkt *pkt, struct net_buf *frag);
*/
u16_t net_tcp_get_chksum(struct net_pkt *pkt, struct net_buf *frag);

/**
* @brief Parse TCP options from network packet.
*
* Parse TCP options, returning MSS value (as that the only one we
* handle so far).
*
* @param pkt Network packet
* @param opt_totlen Total length of options to parse
* @param opts Pointer to TCP options structure. (Each option is updated
* only if present, so the structure must be initialized with the default
* values.)
*
* @return 0 if no error, <0 in case of error
*/
int net_tcp_parse_opts(struct net_pkt *pkt, int opt_totlen,
struct net_tcp_options *opts);

#else

static inline u16_t net_tcp_get_chksum(struct net_pkt *pkt,
Expand Down