vsock/virtio: fix empty payload in tap skb for non-linear buffers

Overview

In the Linux kernel, the following vulnerability has been resolved:

vsock/virtio: fix empty payload in tap skb for non-linear buffers

For non-linear skbs, virtio_transport_build_skb() goes through virtio_transport_copy_nonlinear_skb() to copy the original payload in the new skb to be delivered to the vsockmon tap device. This manually initializes an iov_iter but does not set iov_iter.count. Since the iov_iter is zero-initialized, the copy length is zero and no payload is actually copied to the monitor interface, leaving data un-initialized.

Fix this by removing the linear vs non-linear split and using skb_copy_datagram_iter() with iov_iter_kvec() for all cases, as vhost-vsock already does. This handles both linear and non-linear skbs, properly initializes the iov_iter, and removes the now unused virtio_transport_copy_nonlinear_skb().

While touching this code, let's also check the return value of skb_copy_datagram_iter(), even though it's unlikely to fail.

Affected

• Linux >= 4b0bf10eb077cb43c09746251ef3608d62c45667 < 06747f52ab157591cec7e5623a759473b66ef6f6
• Linux >= 4b0bf10eb077cb43c09746251ef3608d62c45667 < 52da6a74ca3de0fcda60301096b71534b3b18641
• Linux >= 4b0bf10eb077cb43c09746251ef3608d62c45667 < 378b131a25bd1a5ee27ca199fe486c299d5350c5
• Linux >= 4b0bf10eb077cb43c09746251ef3608d62c45667 < 3a3e3d90cbc79600544536723911657730759af3
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.