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[195.231.47.232]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4870bf33d93sm14186498f8f.22.2026.09.17.04.44.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Sep 2026 04:44:18 -0700 (PDT) Message-ID: <8b8de55c-0f97-4048-a759-a59aff74fff6@redhat.com> Date: Thu, 17 Sep 2026 13:44:17 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v3] tcp: annotate lockless access to sk->sk_err To: Quanye Yang , Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , Jakub Kicinski , Simon Horman , "Matthieu Baerts (NGI0)" , Geliang Tang , Mat Martineau , Jiayuan Chen Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260912-mptcp-sk-err-net-v3-1-c41383878bde@proton.me> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260912-mptcp-sk-err-net-v3-1-c41383878bde@proton.me> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/12/26 17:43, Quanye Yang wrote: > BUG: KCSAN: data-race in do_recvmmsg / mptcp_recvmsg > > read-write (marked) to 0xffff8880134d391c of 4 bytes by task 2619 on cpu 1: > instrument_atomic_read_write include/linux/instrumented.h:113 [inline] > sock_error include/net/sock.h:2565 [inline] > do_recvmmsg+0x50c/0x580 net/socket.c:3049 > __sys_recvmmsg net/socket.c:3144 [inline] > __do_sys_recvmmsg net/socket.c:3167 [inline] > __se_sys_recvmmsg net/socket.c:3160 [inline] > __x64_sys_recvmmsg+0x161/0x180 net/socket.c:3160 > x64_sys_call+0x19c7/0x1ca0 arch/x86/include/generated/asm/syscalls_64.h:300 > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] > do_syscall_64+0xde/0x3d0 arch/x86/entry/syscall_64.c:84 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > read to 0xffff8880134d391c of 4 bytes by task 2620 on cpu 0: > tcp_recv_should_stop include/net/tcp.h:3086 [inline] > mptcp_recvmsg+0x54d/0xd50 net/mptcp/protocol.c:2466 > inet_recvmsg+0x204/0x210 net/ipv4/af_inet.c:894 > sock_recvmsg_nosec net/socket.c:1151 [inline] > sock_recvmsg+0x11a/0x140 net/socket.c:1173 > ____sys_recvmsg+0x14b/0x3c0 net/socket.c:2933 > ___sys_recvmsg+0x116/0x160 net/socket.c:2975 > __sys_recvmsg net/socket.c:3008 [inline] > __do_sys_recvmsg net/socket.c:3014 [inline] > __se_sys_recvmsg net/socket.c:3011 [inline] > __x64_sys_recvmsg+0xeb/0x160 net/socket.c:3011 > x64_sys_call+0x1319/0x1ca0 arch/x86/include/generated/asm/syscalls_64.h:48 > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] > do_syscall_64+0xde/0x3d0 arch/x86/entry/syscall_64.c:84 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > value changed: 0x0000006b -> 0x00000000 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 UID: 0 PID: 2620 Comm: syz.2.33 Not tainted 7.2.0-g39d4f32c5d53 #76 PREEMPT(full) > Hardware name: QEMU Ubuntu 26.04 PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1ubuntu1 04/01/2014 > > do_recvmmsg() and getsockopt(SO_ERROR) call sock_error() without the > socket lock. sock_error() clears sk_err with xchg(), which races with > unmarked loads of the same field. > > KCSAN reported the unmarked peek in tcp_recv_should_stop(). The same > lockless writer races with the other plain sk_err reads on the > TCP/MPTCP send, recv and splice paths. > > Annotate those peeks with READ_ONCE(). No extra ordering is needed: > the value is only used to decide whether I/O should stop. This does > not consume sk_err; the check-then-sock_error() TOCTOU on the no-data > paths is a separate issue. > > Suggested-by: Jiayuan Chen > Link: https://lore.kernel.org/netdev/8bbee583-6f21-4817-bfeb-2d60057380a3@linux.dev/ > Reported-by: Matthieu Baerts (NGI0) > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/632 > Signed-off-by: Quanye Yang > --- > Changes in v3: > - drop the Fixes tag and retarget to net-next > - annotate the remaining unmarked sk_err peeks on the TCP/MPTCP > send, recv and splice paths > - Link to v2: https://patch.msgid.link/20260909-mptcp-sk-err-net-v2-1-5044abecac90@proton.me > > Changes in v2: > - add Reported-by and Closes for the MPTCP syzkaller report > - Link to v1: https://patch.msgid.link/20260908-mptcp-sk-err-net-v1-1-da71aaec9afd@proton.me > --- > include/net/tcp.h | 3 ++- > net/core/stream.c | 2 +- > net/ipv4/tcp.c | 6 +++--- > net/ipv4/tcp_bpf.c | 7 +++---- > net/mptcp/protocol.c | 6 +++--- IMHO you should split the tcp and mptcp changes in separate patches. Also the mptcp side has at least one more missing sk->sk_err annotation missing, as reported by sashiko. /P