From ba2c89e0ea74a904d5231643245753d77422e7f5 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Tue, 17 May 2022 11:02:11 -0700 Subject: [PATCH 1/2] mptcp: fix checksum byte order The MPTCP code typecasts the checksum value to u16 and then converts it to big endian while storing the value into the MPTCP option. As a result, the wire encoding for little endian host is wrong, and that causes interoperabilty interoperability issues with other implementation or host with different endianness. Address the issue writing in the packet the unmodified __sum16 value. MPTCP checksum is disabled by default, interoperating with systems with bad mptcp-level csum encoding should cause fallback to TCP. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/275 Fixes: c5b39e26d003 ("mptcp: send out checksum for DSS") Fixes: 390b95a5fb84 ("mptcp: receive checksum for DSS") Signed-off-by: Paolo Abeni Signed-off-by: Mat Martineau Signed-off-by: David S. Miller --- net/mptcp/options.c | 36 ++++++++++++++++++++++++------------ net/mptcp/protocol.h | 2 +- net/mptcp/subflow.c | 2 +- 3 files changed, 26 insertions(+), 14 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 325383646f5c..b548cec86c9d 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -107,7 +107,7 @@ static void mptcp_parse_option(const struct sk_buff *skb, ptr += 2; } if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM) { - mp_opt->csum = (__force __sum16)get_unaligned_be16(ptr); + mp_opt->csum = get_unaligned((__force __sum16 *)ptr); mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD; ptr += 2; } @@ -221,7 +221,7 @@ static void mptcp_parse_option(const struct sk_buff *skb, if (opsize == expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM) { mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD; - mp_opt->csum = (__force __sum16)get_unaligned_be16(ptr); + mp_opt->csum = get_unaligned((__force __sum16 *)ptr); ptr += 2; } @@ -1240,7 +1240,7 @@ static void mptcp_set_rwin(const struct tcp_sock *tp) WRITE_ONCE(msk->rcv_wnd_sent, ack_seq); } -u16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum) +__sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum) { struct csum_pseudo_header header; __wsum csum; @@ -1256,15 +1256,25 @@ u16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum) header.csum = 0; csum = csum_partial(&header, sizeof(header), sum); - return (__force u16)csum_fold(csum); + return csum_fold(csum); } -static u16 mptcp_make_csum(const struct mptcp_ext *mpext) +static __sum16 mptcp_make_csum(const struct mptcp_ext *mpext) { return __mptcp_make_csum(mpext->data_seq, mpext->subflow_seq, mpext->data_len, ~csum_unfold(mpext->csum)); } +static void put_len_csum(u16 len, __sum16 csum, void *data) +{ + __sum16 *sumptr = data + 2; + __be16 *ptr = data; + + put_unaligned_be16(len, ptr); + + put_unaligned(csum, sumptr); +} + void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp, struct mptcp_out_options *opts) { @@ -1340,8 +1350,9 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp, put_unaligned_be32(mpext->subflow_seq, ptr); ptr += 1; if (opts->csum_reqd) { - put_unaligned_be32(mpext->data_len << 16 | - mptcp_make_csum(mpext), ptr); + put_len_csum(mpext->data_len, + mptcp_make_csum(mpext), + ptr); } else { put_unaligned_be32(mpext->data_len << 16 | TCPOPT_NOP << 8 | TCPOPT_NOP, ptr); @@ -1392,11 +1403,12 @@ void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp, goto mp_capable_done; if (opts->csum_reqd) { - put_unaligned_be32(opts->data_len << 16 | - __mptcp_make_csum(opts->data_seq, - opts->subflow_seq, - opts->data_len, - ~csum_unfold(opts->csum)), ptr); + put_len_csum(opts->data_len, + __mptcp_make_csum(opts->data_seq, + opts->subflow_seq, + opts->data_len, + ~csum_unfold(opts->csum)), + ptr); } else { put_unaligned_be32(opts->data_len << 16 | TCPOPT_NOP << 8 | TCPOPT_NOP, ptr); diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index f4ce28bb0fdc..fb40dd676a26 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -723,7 +723,7 @@ void mptcp_token_destroy(struct mptcp_sock *msk); void mptcp_crypto_key_sha(u64 key, u32 *token, u64 *idsn); void mptcp_crypto_hmac_sha(u64 key1, u64 key2, u8 *msg, int len, void *hmac); -u16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum); +__sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum); void __init mptcp_pm_init(void); void mptcp_pm_data_init(struct mptcp_sock *msk); diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 8c37087f0d84..e90fe7eec43a 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -888,7 +888,7 @@ static enum mapping_status validate_data_csum(struct sock *ssk, struct sk_buff * { struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk); u32 offset, seq, delta; - u16 csum; + __sum16 csum; int len; if (!csum_reqd) From ae66fb2ba6c3dcaf8b9612b65aa949a1a4bed150 Mon Sep 17 00:00:00 2001 From: Mat Martineau Date: Tue, 17 May 2022 11:02:12 -0700 Subject: [PATCH 2/2] mptcp: Do TCP fallback on early DSS checksum failure RFC 8684 section 3.7 describes several opportunities for a MPTCP connection to "fall back" to regular TCP early in the connection process, before it has been confirmed that MPTCP options can be successfully propagated on all SYN, SYN/ACK, and data packets. If a peer acknowledges the first received data packet with a regular TCP header (no MPTCP options), fallback is allowed. If the recipient of that first data packet finds a MPTCP DSS checksum error, this provides an opportunity to fail gracefully with a TCP fallback rather than resetting the connection (as might happen if a checksum failure were detected later). This commit modifies the checksum failure code to attempt fallback on the initial subflow of a MPTCP connection, only if it's a failure in the first data mapping. In cases where the peer initiates the connection, requests checksums, is the first to send data, and the peer is sending incorrect checksums (see https://github.com/multipath-tcp/mptcp_net-next/issues/275), this allows the connection to proceed as TCP rather than reset. Fixes: dd8bcd1768ff ("mptcp: validate the data checksum") Acked-by: Paolo Abeni Signed-off-by: Mat Martineau Signed-off-by: David S. Miller --- net/mptcp/protocol.h | 3 ++- net/mptcp/subflow.c | 21 ++++++++++++++++++--- 2 files changed, 20 insertions(+), 4 deletions(-) diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index fb40dd676a26..5655a63aa6a8 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -443,7 +443,8 @@ struct mptcp_subflow_context { can_ack : 1, /* only after processing the remote a key */ disposable : 1, /* ctx can be free at ulp release time */ stale : 1, /* unable to snd/rcv data, do not use for xmit */ - local_id_valid : 1; /* local_id is correctly initialized */ + local_id_valid : 1, /* local_id is correctly initialized */ + valid_csum_seen : 1; /* at least one csum validated */ enum mptcp_data_avail data_avail; u32 remote_nonce; u64 thmac; diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index e90fe7eec43a..be76ada89d96 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -955,11 +955,14 @@ static enum mapping_status validate_data_csum(struct sock *ssk, struct sk_buff * subflow->map_data_csum); if (unlikely(csum)) { MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DATACSUMERR); - subflow->send_mp_fail = 1; - MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPFAILTX); + if (subflow->mp_join || subflow->valid_csum_seen) { + subflow->send_mp_fail = 1; + MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPFAILTX); + } return subflow->mp_join ? MAPPING_INVALID : MAPPING_DUMMY; } + subflow->valid_csum_seen = 1; return MAPPING_OK; } @@ -1141,6 +1144,18 @@ static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ss } } +static bool subflow_can_fallback(struct mptcp_subflow_context *subflow) +{ + struct mptcp_sock *msk = mptcp_sk(subflow->conn); + + if (subflow->mp_join) + return false; + else if (READ_ONCE(msk->csum_enabled)) + return !subflow->valid_csum_seen; + else + return !subflow->fully_established; +} + static bool subflow_check_data_avail(struct sock *ssk) { struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk); @@ -1218,7 +1233,7 @@ fallback: return true; } - if (subflow->mp_join || subflow->fully_established) { + if (!subflow_can_fallback(subflow)) { /* fatal protocol error, close the socket. * subflow_error_report() will introduce the appropriate barriers */