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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45edb5a2c87sm11002245f8f.17.2026.05.27.22.55.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 May 2026 22:55:03 -0700 (PDT) From: David Carlier To: mptcp@lists.linux.dev Cc: matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org, pabeni@redhat.com, David Carlier Subject: [PATCH mptcp-next v9 2/4] mptcp: propagate RECVERR sockopts to subflows Date: Thu, 28 May 2026 06:54:56 +0100 Message-ID: <20260528055459.55133-3-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260528055459.55133-1-devnexen@gmail.com> References: <20260528055459.55133-1-devnexen@gmail.com> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Propagate IP_RECVERR/IP_RECVERR_RFC4884 and IPV6_RECVERR/IPV6_RECVERR_RFC4884 from the MPTCP socket to existing and future subflows. mptcp_setsockopt_recverr() snapshots optval into a local int, applies it to the parent socket via ip_setsockopt() / ipv6_setsockopt(), bumps msk->setsockopt_seq, and forwards to every subflow via mptcp_setsockopt_all_sf(). Newly-joining subflows pick up the four RECVERR bits through sync_socket_options() now that MPTCP_INET_FLAGS_MASK covers them. mptcp_setsockopt_all_sf() skips IPv4 subflows when called with SOL_IPV6: ipv6_setsockopt() on a sock with sk_family != AF_INET6 returns an error, which would abort the loop and leave the remaining subflows desynchronised. This branch was unreachable before this patch (the only caller was TCP_MAXSEG, family-agnostic); it becomes live with the new IPV6_RECVERR / IPV6_RECVERR_RFC4884 caller and the v4-subflow-on-AF_INET6-msk case (v4 MP_JOIN, or userspace PM grafting a v4 subflow onto a v6 msk). Suggested-by: Paolo Abeni Assisted-by: Codex:gpt-5 Signed-off-by: David Carlier --- net/mptcp/sockopt.c | 131 ++++++++++++++++++++++++++++++++++++-------- 1 file changed, 109 insertions(+), 22 deletions(-) diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c index b9cac04a749a..cc510501ccd9 100644 --- a/net/mptcp/sockopt.c +++ b/net/mptcp/sockopt.c @@ -8,6 +8,7 @@ #include #include +#include #include #include #include @@ -19,7 +20,11 @@ #define MPTCP_INET_FLAGS_MASK \ (BIT(INET_FLAGS_TRANSPARENT) | \ BIT(INET_FLAGS_FREEBIND) | \ - BIT(INET_FLAGS_BIND_ADDRESS_NO_PORT)) + BIT(INET_FLAGS_BIND_ADDRESS_NO_PORT) | \ + BIT(INET_FLAGS_RECVERR) | \ + BIT(INET_FLAGS_RECVERR_RFC4884) | \ + BIT(INET_FLAGS_RECVERR6) | \ + BIT(INET_FLAGS_RECVERR6_RFC4884)) static struct sock *__mptcp_tcp_fallback(struct mptcp_sock *msk) { @@ -394,6 +399,82 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname, return -EOPNOTSUPP; } +static int mptcp_setsockopt_all_sf(struct mptcp_sock *msk, int level, + int optname, sockptr_t optval, + unsigned int optlen) +{ + struct mptcp_subflow_context *subflow; + int ret = 0; + + mptcp_for_each_subflow(msk, subflow) { + struct sock *ssk = mptcp_subflow_tcp_sock(subflow); + + /* SOL_IPV6 options on a v4 subflow (v4 MP_JOIN, or userspace PM + * grafting a v4 subflow onto an AF_INET6 msk) would otherwise + * abort the loop with -EAFNOSUPPORT from ipv6_setsockopt(). + */ + if (level == SOL_IPV6 && ssk->sk_family != AF_INET6) + continue; + + ret = tcp_setsockopt(ssk, level, optname, optval, optlen); + if (ret) + break; + } + + if (!ret) + sockopt_seq_inc(msk); + + return ret; +} + +static int mptcp_setsockopt_recverr(struct mptcp_sock *msk, int level, + int optname, sockptr_t optval, + unsigned int optlen) +{ + struct sock *sk = (struct sock *)msk; + int val, ret; + + /* Let ip_setsockopt() / ipv6_setsockopt() validate optval and optlen + * (so 1-byte boolean writes keep the same ABI as plain TCP) and update + * the parent's RECVERR bit. Re-read that bit under lock_sock() and + * push it to the subflows: concurrent setsockopt callers cannot leave + * parent and subflows desynchronized this way. + */ + if (level == SOL_IP) + ret = ip_setsockopt(sk, level, optname, optval, optlen); +#if IS_ENABLED(CONFIG_IPV6) + else if (level == SOL_IPV6) + ret = ipv6_setsockopt(sk, level, optname, optval, optlen); +#endif + else + return -EOPNOTSUPP; + if (ret) + return ret; + + lock_sock(sk); + switch (optname) { + case IP_RECVERR: + val = inet_test_bit(RECVERR, sk); + break; + case IP_RECVERR_RFC4884: + val = inet_test_bit(RECVERR_RFC4884, sk); + break; +#if IS_ENABLED(CONFIG_IPV6) + case IPV6_RECVERR: + val = inet6_test_bit(RECVERR6, sk); + break; + case IPV6_RECVERR_RFC4884: + val = inet6_test_bit(RECVERR6_RFC4884, sk); + break; +#endif + } + + ret = mptcp_setsockopt_all_sf(msk, level, optname, + KERNEL_SOCKPTR(&val), sizeof(val)); + release_sock(sk); + return ret; +} + static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname, sockptr_t optval, unsigned int optlen) { @@ -436,6 +517,10 @@ static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname, release_sock(sk); break; + case IPV6_RECVERR: + case IPV6_RECVERR_RFC4884: + ret = mptcp_setsockopt_recverr(msk, SOL_IPV6, optname, optval, optlen); + break; } return ret; @@ -781,6 +866,9 @@ static int mptcp_setsockopt_v4(struct mptcp_sock *msk, int optname, return mptcp_setsockopt_sol_ip_set(msk, optname, optval, optlen); case IP_TOS: return mptcp_setsockopt_v4_set_tos(msk, optname, optval, optlen); + case IP_RECVERR: + case IP_RECVERR_RFC4884: + return mptcp_setsockopt_recverr(msk, SOL_IP, optname, optval, optlen); } return -EOPNOTSUPP; @@ -808,27 +896,6 @@ static int mptcp_setsockopt_first_sf_only(struct mptcp_sock *msk, int level, int return ret; } -static int mptcp_setsockopt_all_sf(struct mptcp_sock *msk, int level, - int optname, sockptr_t optval, - unsigned int optlen) -{ - struct mptcp_subflow_context *subflow; - int ret = 0; - - mptcp_for_each_subflow(msk, subflow) { - struct sock *ssk = mptcp_subflow_tcp_sock(subflow); - - ret = tcp_setsockopt(ssk, level, optname, optval, optlen); - if (ret) - break; - } - - if (!ret) - sockopt_seq_inc(msk); - - return ret; -} - static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname, sockptr_t optval, unsigned int optlen) { @@ -1473,6 +1540,12 @@ static int mptcp_getsockopt_v4(struct mptcp_sock *msk, int optname, case IP_LOCAL_PORT_RANGE: return mptcp_put_int_option(msk, optval, optlen, READ_ONCE(inet_sk(sk)->local_port_range)); + case IP_RECVERR: + return mptcp_put_int_option(msk, optval, optlen, + inet_test_bit(RECVERR, sk)); + case IP_RECVERR_RFC4884: + return mptcp_put_int_option(msk, optval, optlen, + inet_test_bit(RECVERR_RFC4884, sk)); } return -EOPNOTSUPP; @@ -1493,6 +1566,12 @@ static int mptcp_getsockopt_v6(struct mptcp_sock *msk, int optname, case IPV6_FREEBIND: return mptcp_put_int_option(msk, optval, optlen, inet_test_bit(FREEBIND, sk)); + case IPV6_RECVERR: + return mptcp_put_int_option(msk, optval, optlen, + inet6_test_bit(RECVERR6, sk)); + case IPV6_RECVERR_RFC4884: + return mptcp_put_int_option(msk, optval, optlen, + inet6_test_bit(RECVERR6_RFC4884, sk)); } return -EOPNOTSUPP; @@ -1601,6 +1680,14 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk) src = READ_ONCE(inet_sk(sk)->inet_flags); + /* RECVERR6 bits are only read on AF_INET6 sockets; copying them onto a + * v4 subflow is dead state and diverges from the SOL_IPV6 skip in + * mptcp_setsockopt_all_sf(). + */ + if (ssk->sk_family != AF_INET6) + mask &= ~(BIT(INET_FLAGS_RECVERR6) | + BIT(INET_FLAGS_RECVERR6_RFC4884)); + for_each_set_bit(b, &mask, BITS_PER_LONG) assign_bit(b, &inet_sk(ssk)->inet_flags, src & BIT(b)); -- 2.53.0