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([2001:ee0:4f0c:3090:6fa0:dfe4:1cab:bb2a]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8434b00d4c7sm13288270b3a.40.2026.06.16.07.43.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Jun 2026 07:43:53 -0700 (PDT) Message-ID: <01d04d25-9f6c-4a3e-9292-4f6e26ab2031@gmail.com> Date: Tue, 16 Jun 2026 21:43:46 +0700 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 net v4] virtio-net: fix len check in receive_big() To: Xiang Mei Cc: andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, bestswngs@gmail.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com References: <20260616042837.2249468-1-xmei5@asu.edu> Content-Language: en-US From: Bui Quang Minh In-Reply-To: <20260616042837.2249468-1-xmei5@asu.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/16/26 11:28, Xiang Mei wrote: > receive_big() bounds the device-announced length by > (big_packets_num_skbfrags + 1) * PAGE_SIZE. That is still too loose: > add_recvbuf_big() sets sg[1] to start at offset > sizeof(struct padded_vnet_hdr) into the first page, so the chain > actually carries hdr_len + (PAGE_SIZE - sizeof(padded_vnet_hdr)) + > big_packets_num_skbfrags * PAGE_SIZE bytes -- 20 bytes less than the > check allows for the common hdr_len == 12 case. > > A malicious virtio backend can announce a len in that gap. page_to_skb() > then walks one frag past the page chain, storing a NULL page->private > into skb_shinfo()->frags[MAX_SKB_FRAGS], which is both an out-of-bounds > write past the static frag array and a NULL frag handed up the rx path. > > Bound len by the size add_recvbuf_big() actually advertised. > > Fixes: 0c716703965f ("virtio-net: fix received length check in big packets") I think we should Cc: stable@vger.kernel.org > Reported-by: Weiming Shi > Signed-off-by: Xiang Mei > Reviewed-by: Xuan Zhuo > --- > v4: use easy to understand math to compute the max_len > v3: revoke 2/2 and add Xuan Zhuo's Reviewed-by tag > v2: add additiona check as 2/2 > > drivers/net/virtio_net.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index f4adcfee7a80..8f4562316aaa 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -1999,15 +1999,16 @@ static struct sk_buff *receive_big(struct net_device *dev, > struct virtnet_rq_stats *stats) > { > struct page *page = buf; > + unsigned long max_len = (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE - > + sizeof(struct padded_vnet_hdr) + vi->hdr_len; > struct sk_buff *skb; > > /* Make sure that len does not exceed the size allocated in > * add_recvbuf_big. > */ > - if (unlikely(len > (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE)) { > + if (unlikely(len > max_len)) { > pr_debug("%s: rx error: len %u exceeds allocated size %lu\n", > - dev->name, len, > - (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE); > + dev->name, len, max_len); > goto err; > } > Reviewed-by: Bui Quang Minh Thanks, Quang Minh.