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 C801E3043BE; Wed, 25 Mar 2026 09:04:52 +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=1774429492; cv=none; b=g0Zupkcs1mKBUhvaKR7c1r4a9AwqC4MbzbpmV2xM33u2BlPCDW9D1oWzVpp45GQF3BVDfYRMMsd4gsdXfo5TFconm3FAdtNeRl9CgOwpElFRt9QHdgTvQjN9ZYjIxvuigHWaEfMrQ0Y4SvZLffq1m+t/09ISUdpYHaC29VWD0Sg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774429492; c=relaxed/simple; bh=ui5jwegU4OLOS+z60QNhyMislxj9h80Sy917sqNwYmg=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=c6hk3xLgpX4YKWYEpdkol/mr+2x5O8D91/GiKyoJhnTNkPqaQfJyo4KJ2Bs6sBwM9fa9lTI/j2hIzUP347FOOI2/SJxoLdea1lnQuU1AWi1JTngm+97//by1hVbQRvqMpDY+P98Q8473qvAG1lUhoRm5YchCAyqeFOSBY9o+05A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B9wpEBrV; 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="B9wpEBrV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E291C4CEF7; Wed, 25 Mar 2026 09:04:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774429492; bh=ui5jwegU4OLOS+z60QNhyMislxj9h80Sy917sqNwYmg=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=B9wpEBrVYArfi+e1noQ5LkzwNm6yiIdZiLNIxXS2n8jYNmFLEfdUshnz5GwQ35JCi eoNBKB+fNjk0qCFU4ICkl2BGOBdltLcl2C4+lwh8F5tdNCyUJt6izjoaj5hYVYkraE c1UuVvyvOnZqeGo8Bn3x9VaTnq3gyR9lgB8b8CF2SYtyBF3YNDTukm9mR0it0GbFLL ik5mVvYbsBXUjRYqjc/I5L/pGho8ZLdXaBaVJI3D1KlV47iloPRnk+IAP3dR7TIRje TuwUXs5jfFoNsPiIthMu7ntsQr6RAaUe27r3LBlNB7rR6WEt6Vkbr+G+9IaxdRG+Kr 3i3VuIVaSplQQ== Message-ID: <73d7be31-f066-474d-989b-731b0b15f134@kernel.org> Date: Wed, 25 Mar 2026 10:04:46 +0100 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] mptcp: fix soft lockup in mptcp_recvmsg() Content-Language: fr From: Matthieu Baerts To: Li Xiasong Cc: Mat Martineau , Geliang Tang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org, yuehaibing@huawei.com, zhangchangzhong@huawei.com, weiyongjun1@huawei.com References: <20260324085131.4187473-1-lixiasong1@huawei.com> <12ad947e-f386-4fcc-9043-bf4f95a7db83@kernel.org> <2da353a7-96cf-40ed-9d83-f256ec6965e1@huawei.com> <5d5d6905-4348-409a-9bb3-8eee30f215b1@kernel.org> 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: <5d5d6905-4348-409a-9bb3-8eee30f215b1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 25/03/2026 08:16, Matthieu Baerts wrote: > Hi Li, > > 25 Mar 2026 03:39:13 Li Xiasong : > >> Hi Matt, >> >> On 3/25/2026 3:23 AM, Matthieu Baerts wrote: >>> Hi Li, >>> >>> On 24/03/2026 09:51, 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. >>> >>> (...) >>> >>>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c >>>> index cf1852b99963..401fb2b17685 100644 >>>> --- a/net/mptcp/protocol.c >>>> +++ b/net/mptcp/protocol.c >>>> @@ -2006,7 +2006,7 @@ static void mptcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb) >>>> static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg, >>>>                 size_t len, int flags, int copied_total, >>>>                 struct scm_timestamping_internal *tss, >>>> -               int *cmsg_flags) >>>> +               int *cmsg_flags, struct sk_buff **last) >>>> { >>>>     struct mptcp_sock *msk = mptcp_sk(sk); >>>>     struct sk_buff *skb, *tmp; >>>> @@ -2048,6 +2048,7 @@ static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg, >>>>         } >>>> >>>>         copied += count; >>>> +       *last = skb; >>> >>> My bad, my recommendation to move this assignment here was not a good >>> idea, because 'skb' can be freed at some points after mptcp_eat_recv_skb >>> that can be called here below. >>> >>> If I'm not mistaken, when MSG_PEEK is not used, sk_wait_data() can >>> always be called with NULL for the last skb, because the queue is >>> supposed to be empty. If not, no need to wait for new packets, so NULL >>> can be used. Is that correct? >>> >>> If yes, then I guess 'last' can be initialised to NULL before calling >>> __mptcp_recvmsg_mskq (limit scope), and only set to 'skb' here below, >>> when MSG_PEEK is not used (what you had in v1). >>> >>> Would that work for you? >>> >>> Cheers, >>> Matt >> >> Thanks for the review. I analyzed the concern about the 'last' pointer. >> >> When writing the v2 patch, I did consider this case - in non-MSG_PEEK >> scenario, the skb is freed by mptcp_eat_recv_skb() after setting *last = >> skb, making 'last' point to freed memory. However, in sk_wait_data(), the >> 'last' parameter is only used for pointer comparison: >> >>     skb_peek_tail(&sk->sk_receive_queue) != skb >> >> It only compares the pointer value without dereferencing, so there's no >> actual UAF issue. > > Indeed, but the skb could be (unlikely) reused at that stage. > > For me, the main point is that mptcp_eat_recv_skb() will remove the > skb from the queue. Then NULL can be passed instead, safer. One last thing: as noticed by the AI review, this Fixes tag could be used instead, as it is more tied to MSG_PEEK: Fixes: 8e04ce45a8db ("mptcp: fix MSG_PEEK stream corruption") Cheers, Matt -- Sponsored by the NGI0 Core fund.