mptcp: add mptcp reset option support

The MPTCP reset option allows to carry a mptcp-specific error code that
provides more information on the nature of a connection reset.

Reset option data received gets stored in the subflow context so it can
be sent to userspace via the 'subflow closed' netlink event.

When a subflow is closed, the desired error code that should be sent to
the peer is also placed in the subflow context structure.

If a reset is sent before subflow establishment could complete, e.g. on
HMAC failure during an MP_JOIN operation, the mptcp skb extension is
used to store the reset information.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index cea69c80159599bc93a557639d2986616dd63fb2..16fe34d139c3c42000037c542d646d565a26b0c8 100644 (file)
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -30,8 +30,8 @@ struct mptcp_ext {
                        ack64:1,
                        mpc_map:1,
                        frozen:1,
-                       __unused:1;
-       /* one byte hole */
+                       reset_transient:1;
+       u8              reset_reason:4;
 };
 
 #define MPTCP_RM_IDS_MAX       8
@@ -58,6 +58,8 @@ struct mptcp_out_options {
        struct mptcp_rm_list rm_list;
        u8 join_id;
        u8 backup;
+       u8 reset_reason:4;
+       u8 reset_transient:1;
        u32 nonce;
        u64 thmac;
        u32 token;
@@ -156,6 +158,16 @@ void mptcp_seq_show(struct seq_file *seq);
 int mptcp_subflow_init_cookie_req(struct request_sock *req,
                                  const struct sock *sk_listener,
                                  struct sk_buff *skb);
+
+__be32 mptcp_get_reset_option(const struct sk_buff *skb);
+
+static inline __be32 mptcp_reset_option(const struct sk_buff *skb)
+{
+       if (skb_ext_exist(skb, SKB_EXT_MPTCP))
+               return mptcp_get_reset_option(skb);
+
+       return htonl(0u);
+}
 #else
 
 static inline void mptcp_init(void)
@@ -236,6 +248,8 @@ static inline int mptcp_subflow_init_cookie_req(struct request_sock *req,
 {
        return 0; /* TCP fallback */
 }
+
+static inline __be32 mptcp_reset_option(const struct sk_buff *skb)  { return htonl(0u); }
 #endif /* CONFIG_MPTCP */
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)

diff --git a/include/uapi/linux/mptcp.h b/include/uapi/linux/mptcp.h
index e1172c1ffdfde264a429c5907a6a8235b8cb1abb..8eb3c0844bfff339fa65a5f6ed394b2c81a30098 100644 (file)
--- a/include/uapi/linux/mptcp.h
+++ b/include/uapi/linux/mptcp.h
@@ -174,10 +174,21 @@ enum mptcp_event_attr {
        MPTCP_ATTR_FLAGS,       /* u16 */
        MPTCP_ATTR_TIMEOUT,     /* u32 */
        MPTCP_ATTR_IF_IDX,      /* s32 */
+       MPTCP_ATTR_RESET_REASON,/* u32 */
+       MPTCP_ATTR_RESET_FLAGS, /* u32 */
 
        __MPTCP_ATTR_AFTER_LAST
 };
 
 #define MPTCP_ATTR_MAX (__MPTCP_ATTR_AFTER_LAST - 1)
 
+/* MPTCP Reset reason codes, rfc8684 */
+#define MPTCP_RST_EUNSPEC      0
+#define MPTCP_RST_EMPTCP       1
+#define MPTCP_RST_ERESOURCE    2
+#define MPTCP_RST_EPROHIBIT    3
+#define MPTCP_RST_EWQ2BIG      4
+#define MPTCP_RST_EBADPERF     5
+#define MPTCP_RST_EMIDDLEBOX   6
+
 #endif /* _UAPI_MPTCP_H */

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index dfc6d1c0e710fc521fb831b72f843f8c7e1e602f..312184cead57ed889a1bc73484df43112b20fe76 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -655,14 +655,18 @@ EXPORT_SYMBOL(tcp_v4_send_check);
  *     Exception: precedence violation. We do not implement it in any case.
  */
 
+#ifdef CONFIG_TCP_MD5SIG
+#define OPTION_BYTES TCPOLEN_MD5SIG_ALIGNED
+#else
+#define OPTION_BYTES sizeof(__be32)
+#endif
+
 static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 {
        const struct tcphdr *th = tcp_hdr(skb);
        struct {
                struct tcphdr th;
-#ifdef CONFIG_TCP_MD5SIG
-               __be32 opt[(TCPOLEN_MD5SIG_ALIGNED >> 2)];
-#endif
+               __be32 opt[OPTION_BYTES / sizeof(__be32)];
        } rep;
        struct ip_reply_arg arg;
 #ifdef CONFIG_TCP_MD5SIG
@@ -770,6 +774,17 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
                                     ip_hdr(skb)->daddr, &rep.th);
        }
 #endif
+       /* Can't co-exist with TCPMD5, hence check rep.opt[0] */
+       if (rep.opt[0] == 0) {
+               __be32 mrst = mptcp_reset_option(skb);
+
+               if (mrst) {
+                       rep.opt[0] = mrst;
+                       arg.iov[0].iov_len += sizeof(mrst);
+                       rep.th.doff = arg.iov[0].iov_len / 4;
+               }
+       }
+
        arg.csum = csum_tcpudp_nofold(ip_hdr(skb)->daddr,
                                      ip_hdr(skb)->saddr, /* XXX */
                                      arg.iov[0].iov_len, IPPROTO_TCP, 0);

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index bff22d6ef516acbe0a7d8cdbe1f94d0f5adc9f69..5f47c0b6e3de8e0d59a9f3184b16b6cf6c6a9316 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -879,8 +879,8 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
        struct net *net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
        struct sock *ctl_sk = net->ipv6.tcp_sk;
        unsigned int tot_len = sizeof(struct tcphdr);
+       __be32 mrst = 0, *topt;
        struct dst_entry *dst;
-       __be32 *topt;
        __u32 mark = 0;
 
        if (tsecr)
@@ -890,6 +890,15 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
                tot_len += TCPOLEN_MD5SIG_ALIGNED;
 #endif
 
+#ifdef CONFIG_MPTCP
+       if (rst && !key) {
+               mrst = mptcp_reset_option(skb);
+
+               if (mrst)
+                       tot_len += sizeof(__be32);
+       }
+#endif
+
        buff = alloc_skb(MAX_HEADER + sizeof(struct ipv6hdr) + tot_len,
                         GFP_ATOMIC);
        if (!buff)
@@ -920,6 +929,9 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
                *topt++ = htonl(tsecr);
        }
 
+       if (mrst)
+               *topt++ = mrst;
+
 #ifdef CONFIG_TCP_MD5SIG
        if (key) {
                *topt++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 68361d28dc676517cc45b8526cf36950f6bea07f..4b7119eb2c31c64a04c93639c54c87ad4d4bcfac 100644 (file)
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -305,6 +305,18 @@ static void mptcp_parse_option(const struct sk_buff *skb,
                mp_opt->fastclose = 1;
                break;
 
+       case MPTCPOPT_RST:
+               if (opsize != TCPOLEN_MPTCP_RST)
+                       break;
+
+               if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
+                       break;
+               mp_opt->reset = 1;
+               flags = *ptr++;
+               mp_opt->reset_transient = flags & MPTCP_RST_TRANSIENT;
+               mp_opt->reset_reason = *ptr;
+               break;
+
        default:
                break;
        }
@@ -327,6 +339,7 @@ void mptcp_get_options(const struct sk_buff *skb,
        mp_opt->rm_addr = 0;
        mp_opt->dss = 0;
        mp_opt->mp_prio = 0;
+       mp_opt->reset = 0;
 
        length = (th->doff * 4) - sizeof(struct tcphdr);
        ptr = (const unsigned char *)(th + 1);
@@ -726,6 +739,22 @@ static bool mptcp_established_options_mp_prio(struct sock *sk,
        return true;
 }
 
+static noinline void mptcp_established_options_rst(struct sock *sk, struct sk_buff *skb,
+                                                  unsigned int *size,
+                                                  unsigned int remaining,
+                                                  struct mptcp_out_options *opts)
+{
+       const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+       if (remaining < TCPOLEN_MPTCP_RST)
+               return;
+
+       *size = TCPOLEN_MPTCP_RST;
+       opts->suboptions |= OPTION_MPTCP_RST;
+       opts->reset_transient = subflow->reset_transient;
+       opts->reset_reason = subflow->reset_reason;
+}
+
 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
                               unsigned int *size, unsigned int remaining,
                               struct mptcp_out_options *opts)
@@ -741,11 +770,10 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
        if (unlikely(__mptcp_check_fallback(msk)))
                return false;
 
-       /* prevent adding of any MPTCP related options on reset packet
-        * until we support MP_TCPRST/MP_FASTCLOSE
-        */
-       if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
-               return false;
+       if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) {
+               mptcp_established_options_rst(sk, skb, size, remaining, opts);
+               return true;
+       }
 
        snd_data_fin = mptcp_data_fin_enabled(msk);
        if (mptcp_established_options_mp(sk, skb, snd_data_fin, &opt_size, remaining, opts))
@@ -1062,6 +1090,12 @@ void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
                mp_opt.mp_prio = 0;
        }
 
+       if (mp_opt.reset) {
+               subflow->reset_seen = 1;
+               subflow->reset_reason = mp_opt.reset_reason;
+               subflow->reset_transient = mp_opt.reset_transient;
+       }
+
        if (!mp_opt.dss)
                return;
 
@@ -1289,6 +1323,12 @@ mp_capable_done:
                ptr += 5;
        }
 
+       if (OPTION_MPTCP_RST & opts->suboptions)
+               *ptr++ = mptcp_option(MPTCPOPT_RST,
+                                     TCPOLEN_MPTCP_RST,
+                                     opts->reset_transient,
+                                     opts->reset_reason);
+
        if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
                struct mptcp_ext *mpext = &opts->ext_copy;
                u8 len = TCPOLEN_MPTCP_DSS_BASE;
@@ -1340,3 +1380,20 @@ mp_capable_done:
        if (tp)
                mptcp_set_rwin(tp);
 }
+
+__be32 mptcp_get_reset_option(const struct sk_buff *skb)
+{
+       const struct mptcp_ext *ext = mptcp_get_ext(skb);
+       u8 flags, reason;
+
+       if (ext) {
+               flags = ext->reset_transient;
+               reason = ext->reset_reason;
+
+               return mptcp_option(MPTCPOPT_RST, TCPOLEN_MPTCP_RST,
+                                   flags, reason);
+       }
+
+       return htonl(0u);
+}
+EXPORT_SYMBOL_GPL(mptcp_get_reset_option);

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index cadafafa1049faada7378ce53a7db355a975c6d1..51be6c34b339f38b71260f64bc9ff4f2bdfb1346 100644 (file)
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1687,9 +1687,21 @@ static int mptcp_event_sub_closed(struct sk_buff *skb,
                                  const struct mptcp_sock *msk,
                                  const struct sock *ssk)
 {
+       const struct mptcp_subflow_context *sf;
+
        if (mptcp_event_put_token_and_ssk(skb, msk, ssk))
                return -EMSGSIZE;
 
+       sf = mptcp_subflow_ctx(ssk);
+       if (!sf->reset_seen)
+               return 0;
+
+       if (nla_put_u32(skb, MPTCP_ATTR_RESET_REASON, sf->reset_reason))
+               return -EMSGSIZE;
+
+       if (nla_put_u32(skb, MPTCP_ATTR_RESET_FLAGS, sf->reset_transient))
+               return -EMSGSIZE;
+
        return 0;
 }
 

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 531ee24aa8275f332eb0fb8377c2bde08b9fc0d9..e894345d10c15ac47864937a24640c2afc41c0b5 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3090,14 +3090,18 @@ bool mptcp_finish_join(struct sock *ssk)
        pr_debug("msk=%p, subflow=%p", msk, subflow);
 
        /* mptcp socket already closing? */
-       if (!mptcp_is_fully_established(parent))
+       if (!mptcp_is_fully_established(parent)) {
+               subflow->reset_reason = MPTCP_RST_EMPTCP;
                return false;
+       }
 
        if (!msk->pm.server_side)
                goto out;
 
-       if (!mptcp_pm_allow_new_subflow(msk))
+       if (!mptcp_pm_allow_new_subflow(msk)) {
+               subflow->reset_reason = MPTCP_RST_EPROHIBIT;
                return false;
+       }
 
        /* active connections are already on conn_list, and we can't acquire
         * msk lock here.
@@ -3111,8 +3115,10 @@ bool mptcp_finish_join(struct sock *ssk)
                sock_hold(ssk);
        }
        spin_unlock_bh(&msk->join_list_lock);
-       if (!ret)
+       if (!ret) {
+               subflow->reset_reason = MPTCP_RST_EPROHIBIT;
                return false;
+       }
 
        /* attach to msk socket only after we are sure he will deal with us
         * at close time

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index e8c5ff2b8ace290c769d3e712cbcba05c5041d85..40e9b05856cde1537267a310e22a0d757710f6e9 100644 (file)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -26,6 +26,7 @@
 #define OPTION_MPTCP_RM_ADDR   BIT(8)
 #define OPTION_MPTCP_FASTCLOSE BIT(9)
 #define OPTION_MPTCP_PRIO      BIT(10)
+#define OPTION_MPTCP_RST       BIT(11)
 
 /* MPTCP option subtypes */
 #define MPTCPOPT_MP_CAPABLE    0
@@ -36,6 +37,7 @@
 #define MPTCPOPT_MP_PRIO       5
 #define MPTCPOPT_MP_FAIL       6
 #define MPTCPOPT_MP_FASTCLOSE  7
+#define MPTCPOPT_RST           8
 
 /* MPTCP suboption lengths */
 #define TCPOLEN_MPTCP_MPC_SYN          4
@@ -65,6 +67,7 @@
 #define TCPOLEN_MPTCP_PRIO             3
 #define TCPOLEN_MPTCP_PRIO_ALIGN       4
 #define TCPOLEN_MPTCP_FASTCLOSE                12
+#define TCPOLEN_MPTCP_RST              4
 
 /* MPTCP MP_JOIN flags */
 #define MPTCPOPT_BACKUP                BIT(0)
@@ -94,6 +97,9 @@
 /* MPTCP MP_PRIO flags */
 #define MPTCP_PRIO_BKUP                BIT(0)
 
+/* MPTCP TCPRST flags */
+#define MPTCP_RST_TRANSIENT    BIT(0)
+
 /* MPTCP socket flags */
 #define MPTCP_DATA_READY       0
 #define MPTCP_NOSPACE          1
@@ -123,6 +129,7 @@ struct mptcp_options_received {
        u16     mp_capable : 1,
                mp_join : 1,
                fastclose : 1,
+               reset : 1,
                dss : 1,
                add_addr : 1,
                rm_addr : 1,
@@ -152,6 +159,8 @@ struct mptcp_options_received {
        };
        u64     ahmac;
        u16     port;
+       u8      reset_reason:4;
+       u8      reset_transient:1;
 };
 
 static inline __be32 mptcp_option(u8 subopt, u8 len, u8 nib, u8 field)
@@ -422,6 +431,9 @@ struct mptcp_subflow_context {
        u8      hmac[MPTCPOPT_HMAC_LEN];
        u8      local_id;
        u8      remote_id;
+       u8      reset_seen:1;
+       u8      reset_transient:1;
+       u8      reset_reason:4;
 
        long    delegated_status;
        struct  list_head delegated_node;   /* link into delegated_action, protected by local BH */
@@ -742,7 +754,7 @@ unsigned int mptcp_pm_get_add_addr_accept_max(struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_subflows_max(struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_local_addr_max(struct mptcp_sock *msk);
 
-static inline struct mptcp_ext *mptcp_get_ext(struct sk_buff *skb)
+static inline struct mptcp_ext *mptcp_get_ext(const struct sk_buff *skb)
 {
        return (struct mptcp_ext *)skb_ext_find(skb, SKB_EXT_MPTCP);
 }

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 7a5f50d00d4b73d1fcbe9315dbe84b8443eab424..223d6be5fc3bb068ccf2d1a3327707ed62e89550 100644 (file)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -115,6 +115,16 @@ static bool subflow_use_different_sport(struct mptcp_sock *msk, const struct soc
        return inet_sk(sk)->inet_sport != inet_sk((struct sock *)msk)->inet_sport;
 }
 
+static void subflow_add_reset_reason(struct sk_buff *skb, u8 reason)
+{
+       struct mptcp_ext *mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
+
+       if (mpext) {
+               memset(mpext, 0, sizeof(*mpext));
+               mpext->reset_reason = reason;
+       }
+}
+
 /* Init mptcp request socket.
  *
  * Returns an error code if a JOIN has failed and a TCP reset
@@ -190,8 +200,10 @@ again:
                subflow_req->msk = subflow_token_join_request(req);
 
                /* Can't fall back to TCP in this case. */
-               if (!subflow_req->msk)
+               if (!subflow_req->msk) {
+                       subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
                        return -EPERM;
+               }
 
                if (subflow_use_different_sport(subflow_req->msk, sk_listener)) {
                        pr_debug("syn inet_sport=%d %d",
@@ -400,8 +412,10 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
        } else if (subflow->request_join) {
                u8 hmac[SHA256_DIGEST_SIZE];
 
-               if (!mp_opt.mp_join)
+               if (!mp_opt.mp_join) {
+                       subflow->reset_reason = MPTCP_RST_EMPTCP;
                        goto do_reset;
+               }
 
                subflow->thmac = mp_opt.thmac;
                subflow->remote_nonce = mp_opt.nonce;
@@ -410,6 +424,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 
                if (!subflow_thmac_valid(subflow)) {
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
+                       subflow->reset_reason = MPTCP_RST_EMPTCP;
                        goto do_reset;
                }
 
@@ -438,6 +453,7 @@ fallback:
        return;
 
 do_reset:
+       subflow->reset_transient = 0;
        mptcp_subflow_reset(sk);
 }
 
@@ -654,8 +670,10 @@ create_child:
                 * to reset the context to non MPTCP status.
                 */
                if (!ctx || fallback) {
-                       if (fallback_is_fatal)
+                       if (fallback_is_fatal) {
+                               subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
                                goto dispose_child;
+                       }
 
                        subflow_drop_ctx(child);
                        goto out;
@@ -690,8 +708,10 @@ create_child:
                        struct mptcp_sock *owner;
 
                        owner = subflow_req->msk;
-                       if (!owner)
+                       if (!owner) {
+                               subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT);
                                goto dispose_child;
+                       }
 
                        /* move the msk reference ownership to the subflow */
                        subflow_req->msk = NULL;
@@ -1056,6 +1076,8 @@ fatal:
        smp_wmb();
        ssk->sk_error_report(ssk);
        tcp_set_state(ssk, TCP_CLOSE);
+       subflow->reset_transient = 0;
+       subflow->reset_reason = MPTCP_RST_EMPTCP;
        tcp_send_active_reset(ssk, GFP_ATOMIC);
        subflow->data_avail = 0;
        return false;