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([2001:ee0:4f0e:fb30:37c0:6356:b7b4:119a]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-74ce35d0014sm11883826b3a.67.2025.07.08.07.30.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 07:31:04 -0700 (PDT) Message-ID: Date: Tue, 8 Jul 2025 21:30:58 +0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] virtio-net: fix received length check in big packets From: Bui Quang Minh To: Jason Wang Cc: netdev@vger.kernel.org, "Michael S. Tsirkin" , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Gavin Li , Gavi Teitz , Parav Pandit , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org References: <20250706141150.25344-1-minhquangbui99@gmail.com> <9fa577cf-0999-431c-bfc9-e7911601543c@gmail.com> Content-Language: en-US In-Reply-To: <9fa577cf-0999-431c-bfc9-e7911601543c@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/8/25 21:26, Bui Quang Minh wrote: > On 7/7/25 10:48, Jason Wang wrote: >> On Sun, Jul 6, 2025 at 10:12 PM Bui Quang Minh >> wrote: >>> Since commit 4959aebba8c0 ("virtio-net: use mtu size as buffer length >>> for big packets"), the allocated size for big packets is not >>> MAX_SKB_FRAGS * PAGE_SIZE anymore but depends on negotiated MTU. The >>> number of allocated frags for big packets is stored in >>> vi->big_packets_num_skbfrags. This commit fixes the received length >>> check corresponding to that change. The current incorrect check can >>> lead >>> to NULL page pointer dereference in the below while loop when erroneous >>> length is received. >>> >>> Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for >>> big packets") >>> Signed-off-by: Bui Quang Minh >>> --- >>>   drivers/net/virtio_net.c | 10 +++++++--- >>>   1 file changed, 7 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index 5d674eb9a0f2..ead1cd2fb8af 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -823,7 +823,7 @@ static struct sk_buff *page_to_skb(struct >>> virtnet_info *vi, >>>   { >>>          struct sk_buff *skb; >>>          struct virtio_net_common_hdr *hdr; >>> -       unsigned int copy, hdr_len, hdr_padded_len; >>> +       unsigned int copy, hdr_len, hdr_padded_len, max_remaining_len; >>>          struct page *page_to_free = NULL; >>>          int tailroom, shinfo_size; >>>          char *p, *hdr_p, *buf; >>> @@ -887,12 +887,16 @@ static struct sk_buff *page_to_skb(struct >>> virtnet_info *vi, >>>           * tries to receive more than is possible. This is usually >>>           * the case of a broken device. >>>           */ >>> -       if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) { >>> +       BUG_ON(offset >= PAGE_SIZE); >>> +       max_remaining_len = (unsigned int)PAGE_SIZE - offset; >>> +       max_remaining_len += vi->big_packets_num_skbfrags * PAGE_SIZE; >>> +       if (unlikely(len > max_remaining_len)) { >>>                  net_dbg_ratelimited("%s: too much data\n", >>> skb->dev->name); >>>                  dev_kfree_skb(skb); >>> +               give_pages(rq, page); >> Should this be an independent fix? > > I've realized this is not needed. In receive_big(), if page_to_skb() > returns NULL then give_pages() is called. I'll remove this in next > version. It's a wrong fix actually. Calling give_pages twice will create bug. > >> >>>                  return NULL; >>>          } >>> -       BUG_ON(offset >= PAGE_SIZE); >>> + >>>          while (len) { >>>                  unsigned int frag_size = min((unsigned)PAGE_SIZE - >>> offset, len); >>>                  skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, >>> page, offset, >>> -- >>> 2.43.0 >>> >> Thanks >> >