mptcp: receive checksum for MP_CAPABLE with data

This patch added a new member named csum in struct mptcp_options_received.

When parsing the MP_CAPABLE with data, if the checksum is enabled,
adjust the expected_opsize. If the receiving option length matches the
length with the data checksum, get the checksum value and save it in
mp_opt->csum. And in mptcp_incoming_options, pass it to mpext->csum.

We always parse any csum/nocsum combination and delay the presence check
to later code, to allow reset if missing.

Additionally, in the TX path, use the newly introduce ext field to avoid
MPTCP csum recomputation on TCP retransmission and unneeded csum update
on when setting the data fin_flag.

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
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 33af68eea96f2700464f9d7b6b8911aca2152087..d61bbbf11979217298ef47190f3202bce99d511d 100644 (file)
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -32,7 +32,8 @@ struct mptcp_ext {
                        mpc_map:1,
                        frozen:1,
                        reset_transient:1;
-       u8              reset_reason:4;
+       u8              reset_reason:4,
+                       csum_reqd:1;
 };
 
 #define MPTCP_RM_IDS_MAX       8

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 2e2551590ecd024b742067909b835a7454249ef0..8cbc7586896969242fcea9a835a2e5569d9a08ad 100644 (file)
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -44,7 +44,20 @@ static void mptcp_parse_option(const struct sk_buff *skb,
                        else
                                expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
                }
-               if (opsize != expected_opsize)
+
+               /* Cfr RFC 8684 Section 3.3.0:
+                * If a checksum is present but its use had
+                * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
+                * close the subflow with a RST, as it is not behaving as negotiated.
+                * If a checksum is not present when its use has been negotiated, the
+                * receiver MUST close the subflow with a RST, as it is considered
+                * broken
+                * We parse even option with mismatching csum presence, so that
+                * later in subflow_data_ready we can trigger the reset.
+                */
+               if (opsize != expected_opsize &&
+                   (expected_opsize != TCPOLEN_MPTCP_MPC_ACK_DATA ||
+                    opsize != TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM))
                        break;
 
                /* try to be gentle vs future versions on the initial syn */
@@ -66,11 +79,6 @@ static void mptcp_parse_option(const struct sk_buff *skb,
                 * host requires the use of checksums, checksums MUST be used.
                 * In other words, the only way for checksums not to be used
                 * is if both hosts in their SYNs set A=0."
-                *
-                * Section 3.3.0:
-                * "If a checksum is not present when its use has been
-                * negotiated, the receiver MUST close the subflow with a RST as
-                * it is considered broken."
                 */
                if (flags & MPTCP_CAP_CHECKSUM_REQD)
                        mp_opt->csum_reqd = 1;
@@ -84,7 +92,7 @@ static void mptcp_parse_option(const struct sk_buff *skb,
                        mp_opt->rcvr_key = get_unaligned_be64(ptr);
                        ptr += 8;
                }
-               if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA) {
+               if (opsize >= TCPOLEN_MPTCP_MPC_ACK_DATA) {
                        /* Section 3.1.:
                         * "the data parameters in a MP_CAPABLE are semantically
                         * equivalent to those in a DSS option and can be used
@@ -96,9 +104,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,
                        mp_opt->data_len = get_unaligned_be16(ptr);
                        ptr += 2;
                }
-               pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d",
+               if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM) {
+                       mp_opt->csum = (__force __sum16)get_unaligned_be16(ptr);
+                       mp_opt->csum_reqd = 1;
+                       ptr += 2;
+               }
+               pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d csum=%u",
                         version, flags, opsize, mp_opt->sndr_key,
-                        mp_opt->rcvr_key, mp_opt->data_len);
+                        mp_opt->rcvr_key, mp_opt->data_len, mp_opt->csum);
                break;
 
        case MPTCPOPT_MP_JOIN:
@@ -1118,6 +1131,10 @@ void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
                }
                mpext->data_len = mp_opt.data_len;
                mpext->use_map = 1;
+               mpext->csum_reqd = mp_opt.csum_reqd;
+
+               if (mpext->csum_reqd)
+                       mpext->csum = mp_opt.csum;
        }
 }
 

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 66e5063ac6c939ac90118f0823b66ac66a0abe02..76194babc7543b4e76a0a9c241d3a3fe9f0cc7d6 100644 (file)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -68,6 +68,8 @@
 #define TCPOLEN_MPTCP_FASTCLOSE                12
 #define TCPOLEN_MPTCP_RST              4
 
+#define TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM        (TCPOLEN_MPTCP_DSS_CHECKSUM + TCPOLEN_MPTCP_MPC_ACK_DATA)
+
 /* MPTCP MP_JOIN flags */
 #define MPTCPOPT_BACKUP                BIT(0)
 #define MPTCPOPT_HMAC_LEN      20
@@ -124,6 +126,7 @@ struct mptcp_options_received {
        u64     data_seq;
        u32     subflow_seq;
        u16     data_len;
+       __sum16 csum;
        u16     mp_capable : 1,
                mp_join : 1,
                fastclose : 1,