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([2001:ee0:4f4c:210:5c6f:93f3:3b14:cac4]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b6cf4c13ea9sm2360547a12.16.2025.10.23.08.06.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Oct 2025 08:06:25 -0700 (PDT) Message-ID: <9598c7ae-fda5-4b7f-8e49-751ce7d5eafe@gmail.com> Date: Thu, 23 Oct 2025 22:06:17 +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 received length check in big packets From: Bui Quang Minh To: Xuan Zhuo Cc: "Michael S. Tsirkin" , Jason Wang , =?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, stable@vger.kernel.org, netdev@vger.kernel.org References: <20251022160623.51191-1-minhquangbui99@gmail.com> <1761206734.6182284-1-xuanzhuo@linux.alibaba.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/23/25 21:39, Bui Quang Minh wrote: > On 10/23/25 15:05, Xuan Zhuo wrote: >> On Wed, 22 Oct 2025 23:06:23 +0700, Bui Quang Minh >> wrote: >>> Since commit 4959aebba8c0 ("virtio-net: use mtu size as buffer length >>> for big packets"), when guest gso is off, 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. >>> >>> Because the host announced buffer length can be malicious (e.g. the >>> host >>> vhost_net driver's get_rx_bufs is modified to announce incorrect >>> length), we need a check in virtio_net receive path. Currently, the >>> check is not adapted to the new change which can lead to NULL page >>> pointer dereference in the below while loop when receiving length that >>> is larger than the allocated one. >>> >>> This commit fixes the received length check corresponding to the new >>> change. >>> >>> Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for >>> big packets") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Bui Quang Minh >>> --- >>> Changes in v4: >>> - Remove unrelated changes, add more comments >>> Changes in v3: >>> - Convert BUG_ON to WARN_ON_ONCE >>> Changes in v2: >>> - Remove incorrect give_pages call >>> --- >>>   drivers/net/virtio_net.c | 16 +++++++++++++--- >>>   1 file changed, 13 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index a757cbcab87f..0ffe78b3fd8d 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -852,7 +852,7 @@ 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; >>> @@ -915,13 +915,23 @@ static struct sk_buff *page_to_skb(struct >>> virtnet_info *vi, >>>        * This is here to handle cases when the device erroneously >>>        * tries to receive more than is possible. This is usually >>>        * the case of a broken device. >>> +     * >>> +     * The number of allocated pages for big packet is >>> +     * vi->big_packets_num_skbfrags + 1, the start of first page is >>> +     * for virtio header, the remaining is for data. We need to ensure >>> +     * the remaining len does not go out of the allocated pages. >>> +     * Please refer to add_recvbuf_big for more details on big packet >>> +     * buffer allocation. >>>        */ >>> -    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; >> >> Could we perform this check inside `receive_big` to avoid computing >> `max_remaining_len` altogether? Instead, we could directly compare >> `len` against >> `(vi->big_packets_num_skbfrags + 1) * PAGE_SIZE`. > > That looks better, I'll do that in the next version. > >> And I’d like to know if this check is necessary for other modes as well. > > Other modes have this check as well. check_mergeable_len is used in > mergeable mode. In receive_small, there is a check > >     if (unlikely(len > GOOD_PACKET_LEN)) { >         goto err; I forgot about XDP zerocopy (XSK) mode. In that mode, there is a check in buf_to_xdp.     if (unlikely(len > bufsize)) {         return NULL; Thanks, Quang Minh.