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Tsirkin" , Jason Wang , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , Xuan Zhuo , Will Deacon , kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net v2] vhost/vsock: size receive SKBs from declared payload Date: Sun, 4 Oct 2026 16:34:19 +0900 Message-ID: <20261004073419.4039011-1-4ncienth@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vhost_vsock_alloc_skb() allocates an skb from the total guest descriptor length before reading hdr->len. Descriptor capacity and declared payload length are independent, so a guest can supply a large descriptor with a zero or short payload. On Linux v7.2, 455 zero-payload packets with 64 KiB descriptors retained 30,255,680 bytes on a 256 KiB receive buffer while rx_bytes and buf_used stayed zero. A full-payload control retained 265,984 bytes. The existing SKB_TRUESIZE(0) budget caps skb count but does not account for the descriptor-sized allocation. Repeating this across connections can exhaust host kernel memory. Trimming after allocation is insufficient. Linear skbs retain their full head, while a nonlinear payload exceeding head tailroom can retain its first page fragment. Copy the header into a stack object, validate hdr->len before allocating, and size the skb from the declared payload plus the header. This keeps the allocation proportional to receive accounting for both linear and nonlinear skbs. Use payload_len > len - sizeof(hdr) for validation. This avoids addition overflow on 32-bit hosts and ensures payload_len fits the subsequent int-length copy path. Fixes: ab9aa2f3afc2 ("vhost/vsock: Allocate nonlinear SKBs for handling large receive buffers") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> --- Changes in v2: - validate the header before allocation with an overflow-safe bounds check; - size the skb from declared payload and remove the global trim-helper change; - remove the generic clean-validation statement from the changelog; and - add Will Deacon to Cc. v1: https://lore.kernel.org/netdev/20260930044147.3818241-1-4ncienth@gmail.com/ Built and booted on v7.2 with KASAN, UBSAN and LOCKDEP. A focused allocation/queue probe retained 436,800 and 582,400 bytes for 455 zero and 341-byte packets, versus 30,255,680 bytes for the vulnerable zero case. No KASAN report, WARN, oops or panic occurred. The probe injects skbs in-kernel rather than through a live guest virtqueue. drivers/vhost/vsock.c | 34 ++++++++++++++++------------------ 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c index abed1fbcf66cc5..35f75e23c7497e 100644 --- a/drivers/vhost/vsock.c +++ b/drivers/vhost/vsock.c @@ -364,7 +364,7 @@ static struct sk_buff * vhost_vsock_alloc_skb(struct vhost_virtqueue *vq, unsigned int out, unsigned int in) { - struct virtio_vsock_hdr *hdr; + struct virtio_vsock_hdr hdr; struct iov_iter iov_iter; struct sk_buff *skb; size_t payload_len; @@ -382,34 +382,32 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq, len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM) return NULL; - /* len contains both payload and hdr */ - skb = virtio_vsock_alloc_skb(len, GFP_KERNEL); - if (!skb) - return NULL; - iov_iter_init(&iov_iter, ITER_SOURCE, vq->iov, out, len); - hdr = virtio_vsock_hdr(skb); - nbytes = copy_from_iter(hdr, sizeof(*hdr), &iov_iter); - if (nbytes != sizeof(*hdr)) { + nbytes = copy_from_iter(&hdr, sizeof(hdr), &iov_iter); + if (nbytes != sizeof(hdr)) { vq_err(vq, "Expected %zu bytes for pkt->hdr, got %zu bytes\n", - sizeof(*hdr), nbytes); - kfree_skb(skb); + sizeof(hdr), nbytes); return NULL; } - payload_len = le32_to_cpu(hdr->len); + payload_len = le32_to_cpu(hdr.len); + + /* The pkt is too big or the length in the header is invalid */ + if (payload_len > len - sizeof(hdr)) + return NULL; + + /* Allocate only for the payload declared in the header. */ + skb = virtio_vsock_alloc_skb(payload_len + sizeof(hdr), GFP_KERNEL); + if (!skb) + return NULL; + + memcpy(virtio_vsock_hdr(skb), &hdr, sizeof(hdr)); /* No payload */ if (!payload_len) return skb; - /* The pkt is too big or the length in the header is invalid */ - if (payload_len + sizeof(*hdr) > len) { - kfree_skb(skb); - return NULL; - } - virtio_vsock_skb_put(skb, payload_len); if (skb_copy_datagram_from_iter(skb, 0, &iov_iter, payload_len)) { base-commit: 6dc989ea46b96ce170840174b4a38c4a387fb005 -- 2.55.0