From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE985309F08; Tue, 8 Sep 2026 03:00:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788836411; cv=none; b=XFNJBK4Fn+eSdjshTnQCufrzutqeeoO5CbUzVAKtejtaTvSpVFplA5uYKSVlgZ+Of1Whs3k3H1d5Bu4WNQFz4C47Q/udaN3gOTUkL5/oOxPB/Qy+QQ7E3IvgU5sJGz/tE+YH68VxeVpCHvFfYwlj9rCbm/fDHGvdYHNEy/+EbQY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788836411; c=relaxed/simple; bh=H+3cMeoBF7+P0cb8pgXCTG/4UZ7JdxRxsC+q5xqOw2E=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=ta1oUaocZBU/Q1kNfGDZ6Ik8UN39gpc3j5r83K6ClWevXq/D9FP+v5auLq5Bz9lTvu4ZkMGbF+6vX7zVkN+P9lQRfWBj5lDr1Gns+EJUdtBz24eMqd5XgK9wt/+r94N7bYkoPmw9+JgrGo6Ahwwzqzjbyh8mVUJmXcZhLIqCbQI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Yz5h6b4E; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Yz5h6b4E" Received: by smtp.kernel.org (Postfix) with ESMTPS id 633D0C2BCC7; Tue, 8 Sep 2026 03:00:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1788836411; bh=H+3cMeoBF7+P0cb8pgXCTG/4UZ7JdxRxsC+q5xqOw2E=; h=From:Date:Subject:To:Cc:Reply-To:From; b=Yz5h6b4ElZR+O2sr5VRFguJeYr5hn0SIyaflYW3jUe9k2NWjNVBsavs6/ilWg6Yv+ 2viLIBL8f9oUQV510fvn1azDcWEx0OAVRLvaeof45SWTwtsGjboNSjiam/0F7v5rLL n5JLoKkjkaOsjUJ2BuzrYmOOc6OEoFHqSZTq49+cm4fxXL3YCx6kdIJ4DkYYgDeXT5 uBeca4W0VJhX7WYdlpzk+550VV/uOGAgQknN6fT7Bqg8oPTypWxe5US+fRttepiQtj /OfhvD1f9jSiqr+e+XLpWo+OJ+d/uFSGNb2aP9og+IxpMOwAmTX5/r9QS7J3QW1GJW 8YCT6I0AaQAwg== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AA08C79F9F; Tue, 8 Sep 2026 03:00:11 +0000 (UTC) From: Quanye Yang via B4 Relay Date: Tue, 08 Sep 2026 10:59:58 +0800 Subject: [PATCH net] tcp: fix data-race in tcp_recv_should_stop Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260908-mptcp-sk-err-net-v1-1-da71aaec9afd@proton.me> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/yWMQQ7CMAwEv1L5jCVTFQh8BfUAYQMGESI7IKSqf yfAcVY7M5HDFE67biLDS10fucFy0VG8HPIZrKfG1Eu/lq0EvpcaC/uNYcYZlTcphYAkKxkGalo xJH3/kntqBxr/oz+PV8T6jdE8fwBOehg3eQAAAA== X-Change-ID: 20260908-mptcp-sk-err-net-7ff88ef05044 To: Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , "Matthieu Baerts (NGI0)" , Geliang Tang , Mat Martineau Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Quanye Yang X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1788836410; l=3380; i=quanyeyang@proton.me; s=20260801; h=from:subject:message-id; bh=aVD2Wy+C2Sd5Y8HCYwrqgTQ88TLljMqiVxf6EXpAQ2M=; b=DZaxjjeF5h5EPEKOuqP9tYOn8GIuV4AEQ6hyK5BKm7tPeAcH0LLEUFKTA0wJIMc/HgWmWOsXW 1wUGmPsA+GVB5j0owZlUsT0LJiow8C3G8zvTrN6f6a2GV8siHYkxgjf X-Developer-Key: i=quanyeyang@proton.me; a=ed25519; pk=9L9FrcvzMgxPaBRU6XV0EnqTgjDqVO596rQKSZ9qZoY= X-Endpoint-Received: by B4 Relay for quanyeyang@proton.me/20260801 with auth_id=963 X-Original-From: Quanye Yang Reply-To: quanyeyang@proton.me From: Quanye Yang 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() calls sock_error() without the socket lock. sock_error() clears sk_err with xchg(), which races with the unmarked load in tcp_recv_should_stop(). The same race exists for plain TCP with concurrent recvmmsg() readers; KCSAN reported it on an MPTCP socket because mptcp_recvmsg() uses this helper. Use READ_ONCE() for the lockless peek. No extra ordering is needed: the value is only used to decide whether receiving should stop. This does not consume sk_err; the check-then-sock_error() TOCTOU on the no-data paths is a separate issue. Fixes: eb477fdd6803 ("tcp: add recv_should_stop helper") Signed-off-by: Quanye Yang --- Link: https://lore.kernel.org/all/14749060-d011-41e7-9a4b-754eb5bd9d5b@redhat.com/ --- include/net/tcp.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 436495ff2271..c61d8678eafd 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -3082,7 +3082,8 @@ enum skb_drop_reason tcp_inbound_hash(struct sock *sk, static inline int tcp_recv_should_stop(struct sock *sk) { - return sk->sk_err || + /* sk_err can be cleared locklessly by sock_error(). */ + return READ_ONCE(sk->sk_err) || sk->sk_state == TCP_CLOSE || (sk->sk_shutdown & RCV_SHUTDOWN) || signal_pending(current); --- base-commit: 38b6be101006d3e7af972999f45d4f1e8250587a change-id: 20260908-mptcp-sk-err-net-7ff88ef05044 Best regards, -- Quanye Yang