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 7C650392836; Fri, 27 Mar 2026 12:13:51 +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=1774613631; cv=none; b=GEdMgE02tOfEMshLfByVX2HGz2S9hP/hbojo0CKOw3/tYUNXfXDCKIndHmoAnENtd/c8AhKdL3pBnPaVAjOQ4tzVGsp0Cb+GZygfjWsL7jZQIw0YMhPPGXGHSlQ1si0gkAQvOR6lSmrn+R/9/ZuPs89h3IKkXtwXSarGjTQEsPI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774613631; c=relaxed/simple; bh=FLli+dZ1C9O4tzBSYDltIR6beAvUPfOCqGpu+ZcWdY4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dGVKoROwYySMAvc+BwBmgrX1x03tm5NMs9UTgYUXZpojXKS0YhFAUbr4MUANnL/Uo7sg54Bg8mZUxTpXmnNjhRAwRsfKcx7D48D6EtNRpLOO8cvix86MfPK8RmAiF8lIi1kQZRylxfZL/MmCADpLlQpRhXjMrxIW85F22c+W3lI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Sx0Z0Tq3; 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="Sx0Z0Tq3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33A36C19423; Fri, 27 Mar 2026 12:13:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774613631; bh=FLli+dZ1C9O4tzBSYDltIR6beAvUPfOCqGpu+ZcWdY4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Sx0Z0Tq35iqE1hkxxftnyb4ndneZSGSkda1nyqEi0xjSzdP3HPl7uGj+LsOma3jZk PFGRlRvyPItoWsD9h9JVcFH6659uTKBDVt5L4Tl+chf8Dcqb3BQ+VjcDHMpTNujCw4 jqIUKn18gzw7BoM/ox/gBEWJylIzOLBI/FlQihquS76bZZJvtIfhBNsTwLpzquwGUA O2xavrv1l5yzt6megVI+kJf/2QxPauGJAq3srWRdfHJ1DqiMU2/1FA1UIh1jHNbQE7 xM5non5TgZMja5rwhO0+dx7kyzIelsVRRkjoGriU6V77zAxzni+mEbMbOxKvIJeggx q41P8zm+g76fw== Message-ID: Date: Fri, 27 Mar 2026 13:13:45 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH net v3] mptcp: fix soft lockup in mptcp_recvmsg() Content-Language: fr To: Li Xiasong , Mat Martineau , Geliang Tang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org, yuehaibing@huawei.com, zhangchangzhong@huawei.com, weiyongjun1@huawei.com References: <20260327075544.3622851-1-lixiasong1@huawei.com> 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: <20260327075544.3622851-1-lixiasong1@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Li, On 27/03/2026 08:55, Li Xiasong wrote: > syzbot reported a soft lockup in mptcp_recvmsg() [0]. > > When receiving data with MSG_PEEK | MSG_WAITALL flags, the skb is not > removed from the sk_receive_queue. This causes sk_wait_data() to always > find available data and never perform actual waiting, leading to a soft > lockup. > > Fix this by adding a 'last' parameter to track the last peeked skb. > This allows sk_wait_data() to make informed waiting decisions and prevent > infinite loops when MSG_PEEK is used. Thank you for the new version! (...) > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c > index cf1852b99963..60f6e6a189b7 100644 > --- a/net/mptcp/protocol.c > +++ b/net/mptcp/protocol.c (...) > @@ -2343,7 +2347,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, > > pr_debug("block timeout %ld\n", timeo); > mptcp_cleanup_rbuf(msk, copied); > - err = sk_wait_data(sk, &timeo, NULL); > + err = sk_wait_data(sk, &timeo, last); sashiko is saying [1] this: > Will this cause a soft lockup if all socket buffers in the receive queue > have already been peeked? > > If the queue only contains already-peeked buffers, the loop in > __mptcp_recvmsg_mskq() skips them using a continue statement: > > if (flags & MSG_PEEK) { > /* skip already peeked skbs */ > if (total_data_len + data_len <= copied_total) { > total_data_len += data_len; > continue; > } > > This means last is never assigned and remains NULL. > > When last is NULL, sk_wait_data() checks if the receive queue tail is > not equal to NULL. Since the queue still contains the unconsumed buffers, > this evaluates to true and sk_wait_data() returns immediately without > sleeping. > > Does this result in an infinite loop here when MSG_PEEK and MSG_WAITALL > are used together? I *think* that's a false positive. When MSG_PEEK and MSG_WAITALL are used together, sk_wait_data() will be call with "last" != NULL and will be unblocked when a new data packet (skb->len > 0) is added to the queue. In other words, when walking the queue in __mptcp_recvmsg_mskq, it should never be full of already-peeked skb. Or did I miss something? If yes, "*last = skb" could be added before the "continue". If no, this patch can be applied in 'net' directly: Reviewed-by: Matthieu Baerts (NGI0) [1] https://sashiko.dev/#/patchset/20260327075544.3622851-1-lixiasong1%40huawei.com Cheers, Matt -- Sponsored by the NGI0 Core fund.