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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45eaa7cf23bsm4086708f8f.5.2026.05.21.10.13.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 10:13:50 -0700 (PDT) Date: Thu, 21 May 2026 18:13:48 +0100 From: David Laight To: Stefano Garzarella Cc: netdev@vger.kernel.org, Xuan Zhuo , Simon Horman , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Jakub Kicinski , Eugenio =?UTF-8?B?UMOpcmV6?= , Paolo Abeni , "Michael S. Tsirkin" , "David S. Miller" , Jason Wang , Stefan Hajnoczi , Eric Dumazet , stable@vger.kernel.org Subject: Re: [PATCH net] vsock/virtio: fix skb overhead overflow on 32-bit builds Message-ID: <20260521181348.3d61858e@pumpkin> In-Reply-To: <20260521124732.125771-1-sgarzare@redhat.com> References: <20260521124732.125771-1-sgarzare@redhat.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 21 May 2026 14:47:32 +0200 Stefano Garzarella wrote: > From: Stefano Garzarella > > On 32-bit architectures, both skb_queue_len() and SKB_TRUESIZE(0) evaluate > to 32-bit values. The multiplication can overflow before being assigned to > the u64 skb_overhead variable, making the skb overhead check ineffective. > > Cast skb_queue_len() to u64 so the multiplication is always performed in > 64-bit arithmetic. > > This issue was reported by Sashiko while reviewing another patch. > > Fixes: 059b7dbd20a6 ("vsock/virtio: fix potential unbounded skb queue") > Closes: https://sashiko.dev/#/patchset/20260518090656.134588-1-sgarzare%40redhat.com > Cc: stable@vger.kernel.org > Signed-off-by: Stefano Garzarella > --- > net/vmw_vsock/virtio_transport_common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > index df3b418e0392..71198bf23fc4 100644 > --- a/net/vmw_vsock/virtio_transport_common.c > +++ b/net/vmw_vsock/virtio_transport_common.c > @@ -417,7 +417,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, > u32 len) > { > - u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0); > + u64 skb_overhead = ((u64)skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0); I was thinking this should use mul_u32_u32(). But that is all moot. 'skb_overhead' is a memory size in bytes, 'unsigned long' it more than big enough. No need for 64bit maths on 32bit. -- David > > /* Allow at most buf_alloc * 2 total budget (payload + overhead), > * similar to how SO_RCVBUF is doubled to reserve space for sk_buff