netdev - Re: [PATCH net] virtio/vsock: Fix uninit-value in virtio_transport_recv

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Date: Fri, 27 Oct 2023 10:50:50 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Shigeru Yoshida <syoshida@...hat.com>, stefanha@...hat.com, davem@...emloft.net, 
	kuba@...nel.org, pabeni@...hat.com, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bobby.eshleman@...edance.com, 
	bobbyeshleman@...il.com
Subject: Re: [PATCH net] virtio/vsock: Fix uninit-value in virtio_transport_recv_pkt()

On Fri, Oct 27, 2023 at 10:18 AM Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Fri, Oct 27, 2023 at 10:01 AM Stefano Garzarella <sgarzare@...hat.com> wrote:
> >
> > 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@...hat.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 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@...hat.com>
>
> syzbot just reported the same [1], should we add the following tag?
>
> Reported-by: syzbot+0c8ce1da0ac31abbadcd@...kaller.appspotmail.com
>
> [1] https://lore.kernel.org/netdev/00000000000008b2940608ae3ce9@google.com/

Yes, I was about to add this tag as well, but you were fast ;)

Reviewed-by: Eric Dumazet <edumazet@...gle.com>