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[195.231.44.239]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4994a0f7bf4sm69568615e9.11.2026.08.04.02.26.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Aug 2026 02:26:59 -0700 (PDT) Message-ID: <6a2958d9-5d16-404a-ac02-21940e90162d@redhat.com> Date: Tue, 4 Aug 2026 11:26:57 +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 Subject: Re: [PATCH v3] vsock: use sock_error() to consume sk_err after a failed connect To: phind.uet@gmail.com, Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , Andy King , George Zhang , Dmitry Torokhov Cc: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com, Wupeng Ma , virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260730081843.287563-1-phind.uet@gmail.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260730081843.287563-1-phind.uet@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/30/26 10:18 AM, phind.uet@gmail.com wrote: > From: Nguyen Dinh Phi > > Syzbot report an issue which can be reproduced with these steps: > > r0 = socket(AF_VSOCK, SOCK_STREAM, 0) > bind(r0, {VMADDR_CID_ANY, PORT}) > connect(r0, {VMADDR_CID_LOCAL, PORT}) -> -1, EPROTO (self-connect) > listen(r0, backlog) -> 0 > r1 = socket(AF_VSOCK, SOCK_STREAM, 0) > connect(r1, {VMADDR_CID_LOCAL, PORT}) -> 0 > accept(r0) -> -1, EPROTO (stale sk_err) > > Basically, it creates a socket (r0) and triggers a self-connect after > binding it. This self-connect fails with EPROTO because it loops back to > r0 while the socket is still in the TCP_SYN_SENT state, causing it to be > incorrectly dispatched to the connecting-client path. The unexpected > packet type encountered there sets sk_err to EPROTO. > > After that, it invokes a listen() call on the same socket. This listen() > call succeeds because the kernel's listening path never inspects or > clears sk_err. Then, a new socket (r1) is created as a normal client and > connects to r0. However, vsock_accept() rejects this incoming connection > because the listener's sk_err still holds the EPROTO error from the > earlier failed self-connect. > > This rejection causes the child socket created for r1's connection to > never be freed on virtio or hyperv transports; only the VMCI transport > implements pending_work to revisit and clean up a rejected socket > > Fix the issue by using sock_error() to read the sk_err to prevent the > rejection branch from occurring in this scenario. > > sock_error() atomically reads and clears sk_err, ensuring the error is > consumed when vsock_connect() returns and cannot affect subsequent > operations on the same socket. This matches the established pattern > used by other protocol connect() implementations in the network > stack like __inet_stream_connect(), tipc_wait_for_connect()... > > Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=1b2c9c4a0f8708082678 > Fixes: d021c344051af ("VSOCK: Introduce VM Sockets") > Signed-off-by: Nguyen Dinh Phi > Tested-by: Wupeng Ma Sashiko nipa points out that the race still exits: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260730081843.287563-1-phind.uet%40gmail.com /P