linux-kernel - [PATCH 1/5] vhost/vsock: Avoid allocating arbitrarily-sized SKBs

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Message-Id: <20250625131543.5155-2-will@kernel.org>
Date: Wed, 25 Jun 2025 14:15:39 +0100
From: Will Deacon <will@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Will Deacon <will@...nel.org>,
	Keir Fraser <keirf@...gle.com>,
	Steven Moreland <smoreland@...gle.com>,
	Frederick Mayle <fmayle@...gle.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	netdev@...r.kernel.org,
	virtualization@...ts.linux.dev
Subject: [PATCH 1/5] vhost/vsock: Avoid allocating arbitrarily-sized SKBs

vhost_vsock_alloc_skb() returns NULL for packets advertising a length
larger than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE in the packet header. However,
this is only checked once the SKB has been allocated and, if the length
in the packet header is zero, the SKB may not be freed immediately.

Hoist the size check before the SKB allocation so that an iovec larger
than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + the header size is rejected
outright. The subsequent check on the length field in the header can
then simply check that the allocated SKB is indeed large enough to hold
the packet.

Signed-off-by: Will Deacon <will@...nel.org>
---
 drivers/vhost/vsock.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 802153e23073..66a0f060770e 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -344,6 +344,9 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
 
 	len = iov_length(vq->iov, out);
 
+	if (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)
@@ -367,8 +370,7 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
 		return skb;
 
 	/* The pkt is too big or the length in the header is invalid */
-	if (payload_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE ||
-	    payload_len + sizeof(*hdr) > len) {
+	if (payload_len + sizeof(*hdr) > len) {
 		kfree_skb(skb);
 		return NULL;
 	}
-- 
2.50.0.714.g196bf9f422-goog