From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 055CF46C4CC; Wed, 9 Sep 2026 09:08:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788944889; cv=none; b=iteJ7McumY9ASru4IB0Wa/hz2eKEUz6b2kl5k35+x06v2H3uFl9Cwa6A3Evv4gnBzT2Ih9jNoxYO8CsBHE2s0Rn4FQi0u5LIZgMXFVRH9ratEmRi+m8Hl3i0wC2eC0uvyZWScbBX5nB1snwskZY3dRNP1IBE6VMiPY+MtoSZP+o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788944889; c=relaxed/simple; bh=5wRF7TRW52v6iM/t+CctJ9Yw2DGOgUE70RFWbI6LmVw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oFo2InIBTUAZf5OFB6UJaEHKhUviLLsdeS5EbasXWysidgGsXblCKPuWj81x0PEb0FpLPFNJXBVOcJnGzw4DwyAWgI0rPTebgznjBqCkp4yOQuInAMSMJpexorSXpMvkncy8eupVmOwvUKl5/gYhCD7XpBKEF8VfXluUU5f/Ujg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cQ8GOymJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cQ8GOymJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 23C9F1F00A3A; Wed, 9 Sep 2026 09:08:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788944887; bh=ikuyhdzrRTHbXh9Rv6iCOPsdsIpNolnvd/NEcrSB7ws=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cQ8GOymJdzZblgxf4OYQEVE/awuSct+wlDX8T2nATx7nfJ3JEInMX289INZHNlhyf fAAY9JvOxyfYMRV11pek1qtgDrpgzHe4VtLvJhHsiWItJePhCF9RzLsff798eeStE2 ezFSmFmtFaNnWTFcNgnpaj4Gtwg5VhwebYzETEX3UZ20vnu518N8xOWHxBteWV3gcf EZHvJ1yoxrqZLsSB+dOubuOI1frz5E2Lr84vJpUVJJ9v4YfvrdMBrFj1maIb4ZEl8v HngSBzetAIxzWkKh67dNTsnIWc9ThPisHK1CUgilXTfZw/Ey0njFuaYRZpo+klUfjr NiRduo0MWPoMw== Message-ID: Date: Wed, 9 Sep 2026 11:08:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH net v2] tcp: fix data-race in tcp_recv_should_stop Content-Language: fr To: Jiayuan Chen , quanyeyang@proton.me, Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , Geliang Tang , Mat Martineau Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260909-mptcp-sk-err-net-v2-1-5044abecac90@proton.me> <8bbee583-6f21-4817-bfeb-2d60057380a3@linux.dev> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; keydata= xsFNBFXj+ekBEADxVr99p2guPcqHFeI/JcFxls6KibzyZD5TQTyfuYlzEp7C7A9swoK5iCvf YBNdx5Xl74NLSgx6y/1NiMQGuKeu+2BmtnkiGxBNanfXcnl4L4Lzz+iXBvvbtCbynnnqDDqU c7SPFMpMesgpcu1xFt0F6bcxE+0ojRtSCZ5HDElKlHJNYtD1uwY4UYVGWUGCF/+cY1YLmtfb WdNb/SFo+Mp0HItfBC12qtDIXYvbfNUGVnA5jXeWMEyYhSNktLnpDL2gBUCsdbkov5VjiOX7 CRTkX0UgNWRjyFZwThaZADEvAOo12M5uSBk7h07yJ97gqvBtcx45IsJwfUJE4hy8qZqsA62A nTRflBvp647IXAiCcwWsEgE5AXKwA3aL6dcpVR17JXJ6nwHHnslVi8WesiqzUI9sbO/hXeXw TDSB+YhErbNOxvHqCzZEnGAAFf6ges26fRVyuU119AzO40sjdLV0l6LE7GshddyazWZf0iac nEhX9NKxGnuhMu5SXmo2poIQttJuYAvTVUNwQVEx/0yY5xmiuyqvXa+XT7NKJkOZSiAPlNt6 VffjgOP62S7M9wDShUghN3F7CPOrrRsOHWO/l6I/qJdUMW+MHSFYPfYiFXoLUZyPvNVCYSgs 3oQaFhHapq1f345XBtfG3fOYp1K2wTXd4ThFraTLl8PHxCn4ywARAQABzSRNYXR0aGlldSBC YWVydHMgPG1hdHR0YmVAa2VybmVsLm9yZz7CwZEEEwEIADsCGwMFCwkIBwIGFQoJCAsCBBYC AwECHgECF4AWIQToy4X3aHcFem4n93r2t4JPQmmgcwUCZUDpDAIZAQAKCRD2t4JPQmmgcz33 EACjROM3nj9FGclR5AlyPUbAq/txEX7E0EFQCDtdLPrjBcLAoaYJIQUV8IDCcPjZMJy2ADp7 /zSwYba2rE2C9vRgjXZJNt21mySvKnnkPbNQGkNRl3TZAinO1Ddq3fp2c/GmYaW1NWFSfOmw MvB5CJaN0UK5l0/drnaA6Hxsu62V5UnpvxWgexqDuo0wfpEeP1PEqMNzyiVPvJ8bJxgM8qoC cpXLp1Rq/jq7pbUycY8GeYw2j+FVZJHlhL0w0Zm9CFHThHxRAm1tsIPc+oTorx7haXP+nN0J iqBXVAxLK2KxrHtMygim50xk2QpUotWYfZpRRv8dMygEPIB3f1Vi5JMwP4M47NZNdpqVkHrm jvcNuLfDgf/vqUvuXs2eA2/BkIHcOuAAbsvreX1WX1rTHmx5ud3OhsWQQRVL2rt+0p1DpROI 3Ob8F78W5rKr4HYvjX2Inpy3WahAm7FzUY184OyfPO/2zadKCqg8n01mWA9PXxs84bFEV2mP VzC5j6K8U3RNA6cb9bpE5bzXut6T2gxj6j+7TsgMQFhbyH/tZgpDjWvAiPZHb3sV29t8XaOF BwzqiI2AEkiWMySiHwCCMsIH9WUH7r7vpwROko89Tk+InpEbiphPjd7qAkyJ+tNIEWd1+MlX ZPtOaFLVHhLQ3PLFLkrU3+Yi3tXqpvLE3gO3LM7BTQRV4/npARAA5+u/Sx1n9anIqcgHpA7l 5SUCP1e/qF7n5DK8LiM10gYglgY0XHOBi0S7vHppH8hrtpizx+7t5DBdPJgVtR6SilyK0/mp 9nWHDhc9rwU3KmHYgFFsnX58eEmZxz2qsIY8juFor5r7kpcM5dRR9aB+HjlOOJJgyDxcJTwM 1ey4L/79P72wuXRhMibN14SX6TZzf+/XIOrM6TsULVJEIv1+NdczQbs6pBTpEK/G2apME7vf mjTsZU26Ezn+LDMX16lHTmIJi7Hlh7eifCGGM+g/AlDV6aWKFS+sBbwy+YoS0Zc3Yz8zrdbi Kzn3kbKd+99//mysSVsHaekQYyVvO0KD2KPKBs1S/ImrBb6XecqxGy/y/3HWHdngGEY2v2IP Qox7mAPznyKyXEfG+0rrVseZSEssKmY01IsgwwbmN9ZcqUKYNhjv67WMX7tNwiVbSrGLZoqf Xlgw4aAdnIMQyTW8nE6hH/Iwqay4S2str4HZtWwyWLitk7N+e+vxuK5qto4AxtB7VdimvKUs x6kQO5F3YWcC3vCXCgPwyV8133+fIR2L81R1L1q3swaEuh95vWj6iskxeNWSTyFAVKYYVskG V+OTtB71P1XCnb6AJCW9cKpC25+zxQqD2Zy0dK3u2RuKErajKBa/YWzuSaKAOkneFxG3LJIv Hl7iqPF+JDCjB5sAEQEAAcLBXwQYAQIACQUCVeP56QIbDAAKCRD2t4JPQmmgc5VnD/9YgbCr HR1FbMbm7td54UrYvZV/i7m3dIQNXK2e+Cbv5PXf19ce3XluaE+wA8D+vnIW5mbAAiojt3Mb 6p0WJS3QzbObzHNgAp3zy/L4lXwc6WW5vnpWAzqXFHP8D9PTpqvBALbXqL06smP47JqbyQxj Xf7D2rrPeIqbYmVY9da1KzMOVf3gReazYa89zZSdVkMojfWsbq05zwYU+SCWS3NiyF6QghbW voxbFwX1i/0xRwJiX9NNbRj1huVKQuS4W7rbWA87TrVQPXUAdkyd7FRYICNW+0gddysIwPoa KrLfx3Ba6Rpx0JznbrVOtXlihjl4KV8mtOPjYDY9u+8x412xXnlGl6AC4HLu2F3ECkamY4G6 UxejX+E6vW6Xe4n7H+rEX5UFgPRdYkS1TA/X3nMen9bouxNsvIJv7C6adZmMHqu/2azX7S7I vrxxySzOw9GxjoVTuzWMKWpDGP8n71IFeOot8JuPZtJ8omz+DZel+WCNZMVdVNLPOd5frqOv mpz0VhFAlNTjU1Vy0CnuxX3AM51J8dpdNyG0S8rADh6C8AKCDOfUstpq28/6oTaQv7QZdge0 JY6dglzGKnCi/zsmp2+1w559frz4+IC7j/igvJGX4KDDKUs0mlld8J2u2sBXv7CGxdzQoHaz lzVbFe7fduHbABmYz9cefQpO7wDE/Q== Organization: NGI0 Core In-Reply-To: <8bbee583-6f21-4817-bfeb-2d60057380a3@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Jiayuan, On 09/09/2026 04:57, Jiayuan Chen wrote: > > On 9/9/26 10:05 AM, Quanye Yang via B4 Relay wrote: >> 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") > > > Is the Fixes tag right? eb477fdd6803 only moved the existing check > into a helper, the plain read was already there before. > > >> Reported-by: Matthieu Baerts (NGI0) >> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/632 >> Signed-off-by: Quanye Yang >> --- >> Link: https://lore.kernel.org/all/14749060- >> d011-41e7-9a4b-754eb5bd9d5b@redhat.com/ >> --- >> 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 ++- >>   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); > > > The lockless writers are sock_error() from SO_ERROR and recvmmsg(), > so every plain read of sk_err on a TCP socket has the same race, not > only this helper: >     tcp_recvmsg_locked >     tcp_sendmsg_locked >     tcp_splice_read >     sk_stream_wait_memory >     tcp_bpf_sendmsg >     tcp_bpf_recvmsg_parser >     mptcp_splice_read >     mptcp_recvmsg > > I'd drop the Fixes tag, target net-next and annotate all of them like > e13ec3da05d1, instead of pointing at a MPTCP commit. > > Eric, Matthieu, does that sound OK? Sounds good to me to target net-next without the Fixes tag. Cheers, Matt -- Sponsored by the NGI0 Core fund.