Re: [PATCH net v2] virtio/vsock: Fix uninit-value in virtio_transport_recv_pkt()

[David Wei <dw@davidwei.uk>]

On 2023-11-04 08:05, 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_init_hdr()`. This patch resolves the issue by
> initializing these fields during allocation.
> 
> Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
> Reported-and-tested-by: syzbot+0c8ce1da0ac31abbadcd@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=0c8ce1da0ac31abbadcd
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> ---
> v1->v2:
> - Rebase on the latest net tree
> https://lore.kernel.org/all/20231026150154.3536433-1-syoshida@redhat.com/
> ---
>  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 e22c81435ef7..dc65dd4d26df 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -130,6 +130,8 @@ static void virtio_transport_init_hdr(struct sk_buff *skb,
>  	hdr->dst_port	= cpu_to_le32(dst_port);
>  	hdr->flags	= cpu_to_le32(info->flags);
>  	hdr->len	= cpu_to_le32(payload_len);
> +	hdr->buf_alloc	= cpu_to_le32(0);
> +	hdr->fwd_cnt	= cpu_to_le32(0);

This change looks good to me.

I did notice that payload_len in virtio_transport_init_hdr is size_t but
len in struct virtio_vsock_hdr is __le32. But I don't think this is an
issue other than wasting some stack space, though.

>  }
>  
>  static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb,