Re: [PATCH net] virtio/vsock: Fix uninit-value in virtio_transport_recv_pkt()

[Stefano Garzarella]

On Fri, Oct 27, 2023 at 12:01:54AM +0900, Shigeru Yoshida wrote:
> KMSAN reported the following uninit-value access issue:
>
> =====================================================
> BUG: KMSAN: uninit-value in virtio_transport_recv_pkt+0x1dfb/0x26a0 net/vmw_vsock/virtio_transport_common.c:1421
> virtio_transport_recv_pkt+0x1dfb/0x26a0 net/vmw_vsock/virtio_transport_common.c:1421
> vsock_loopback_work+0x3bb/0x5a0 net/vmw_vsock/vsock_loopback.c:120
> process_one_work kernel/workqueue.c:2630 [inline]
> process_scheduled_works+0xff6/0x1e60 kernel/workqueue.c:2703
> worker_thread+0xeca/0x14d0 kernel/workqueue.c:2784
> kthread+0x3cc/0x520 kernel/kthread.c:388
> ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
>
> Uninit was stored to memory at:
> virtio_transport_space_update net/vmw_vsock/virtio_transport_common.c:1274 [inline]
> virtio_transport_recv_pkt+0x1ee8/0x26a0 net/vmw_vsock/virtio_transport_common.c:1415
> vsock_loopback_work+0x3bb/0x5a0 net/vmw_vsock/vsock_loopback.c:120
> process_one_work kernel/workqueue.c:2630 [inline]
> process_scheduled_works+0xff6/0x1e60 kernel/workqueue.c:2703
> worker_thread+0xeca/0x14d0 kernel/workqueue.c:2784
> kthread+0x3cc/0x520 kernel/kthread.c:388
> ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
>
> Uninit was created at:
> slab_post_alloc_hook+0x105/0xad0 mm/slab.h:767
> slab_alloc_node mm/slub.c:3478 [inline]
> kmem_cache_alloc_node+0x5a2/0xaf0 mm/slub.c:3523
> kmalloc_reserve+0x13c/0x4a0 net/core/skbuff.c:559
> __alloc_skb+0x2fd/0x770 net/core/skbuff.c:650
> alloc_skb include/linux/skbuff.h:1286 [inline]
> virtio_vsock_alloc_skb include/linux/virtio_vsock.h:66 [inline]
> virtio_transport_alloc_skb+0x90/0x11e0 net/vmw_vsock/virtio_transport_common.c:58
> virtio_transport_reset_no_sock net/vmw_vsock/virtio_transport_common.c:957 [inline]
> virtio_transport_recv_pkt+0x1279/0x26a0 net/vmw_vsock/virtio_transport_common.c:1387
> vsock_loopback_work+0x3bb/0x5a0 net/vmw_vsock/vsock_loopback.c:120
> process_one_work kernel/workqueue.c:2630 [inline]
> process_scheduled_works+0xff6/0x1e60 kernel/workqueue.c:2703
> worker_thread+0xeca/0x14d0 kernel/workqueue.c:2784
> kthread+0x3cc/0x520 kernel/kthread.c:388
> ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
>
> CPU: 1 PID: 10664 Comm: kworker/1:5 Not tainted 6.6.0-rc3-00146-g9f3ebbef746f #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
> Workqueue: vsock-loopback vsock_loopback_work
> =====================================================
>
> The following simple reproducer can cause the issue described above:
>
> int main(void)
> {
>  int sock;
>  struct sockaddr_vm addr = {
>    .svm_family = AF_VSOCK,
>    .svm_cid = VMADDR_CID_ANY,
>    .svm_port = 1234,
>  };
>
>  sock = socket(AF_VSOCK, SOCK_STREAM, 0);
>  connect(sock, (struct sockaddr *)&addr, sizeof(addr));
>  return 0;
> }
>
> This issue occurs because the `buf_alloc` and `fwd_cnt` fields of the
> `struct virtio_vsock_hdr` are not initialized when a new skb is allocated
> in `virtio_transport_alloc_skb()`. This patch resolves the issue by
> initializing these fields during allocation.
>
> Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")

CCin Bobby, the original author, for any additional comments/checks.

Yeah, I see, before that commit we used kzalloc() to allocate the
header so we forgot to reset these 2 fields, and checking they are
the only 2 missing.

I was thinking of putting a memset(hdr, 0, sizeof(*hdr)) in
virtio_vsock_alloc_skb() but I think it's just extra unnecessary work,
since here we set all the fields (thanks to this fix), in vhost/vsock.c
we copy all the header we receive from the guest and in
virtio_transport.c we already set it all to 0 because we are
preallocating the receive buffers.

So I'm fine with this fix!

> Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
> ---
> net/vmw_vsock/virtio_transport_common.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 352d042b130b..102673bef189 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -68,6 +68,8 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 	hdr->dst_port	= cpu_to_le32(dst_port);
> 	hdr->flags	= cpu_to_le32(info->flags);
> 	hdr->len	= cpu_to_le32(len);
> +	hdr->buf_alloc	= cpu_to_le32(0);
> +	hdr->fwd_cnt	= cpu_to_le32(0);
>
> 	if (info->msg && len > 0) {
> 		payload = skb_put(skb, len);
> --
> 2.41.0

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

Thanks,
Stefano