Re: [PATCH net] vsock: Fix memory leak in vmci_transport_recv_dgram_cb()

[Stefano Garzarella]

On Wed, Oct 07, 2026 at 02:37:47PM +0000, Ilia Gavrilov wrote:
> During the closure of a datagram socket, the vmci_transport_recv_dgram_cb()
> function may be called, which will add the packets
> to the socket's backlog; then, after the receive queue is cleared,
> the __release_sock() function will move the packet back from the socket's
> backlog to the receive queue, which will lead to a memory leak.
>
> sock_close
>  __sock_release
>    __vsock_release
>      // take ownership by user-space
>      lock_sock_nested
>      sock_set_flag(sk, SOCK_DEAD)
>      vmci_transport_release
>                                      vmci_dispatch_dgs
>                                        vmci_datagram_invoke_guest_handler
>                                          vmci_transport_recv_dgram_cb
>                                            sk_receive_skb
>                                              if (!sock_owned_by_user(sk))
>                                                  [...]
>                                         (!)  else if sk_add_backlog()
>                                                  [...]
>  (!) skb_queue_purge(&sk->sk_receive_queue)
>
>      release_sock
>        __release_sock
>          // move all packets from the backlog
>          // to the receive queue
>   (!)    sk_backlog_rcv
>            vsock_queue_rcv_skb
>            [...]
>              __sock_queue_rcv_skb
>                if (!sock_flag(sk, SOCK_DEAD))
>                  // Since the socket is "dead", the function will not
>                  // be called
>                  sk->sk_data_ready(sk)
>        sock_release_ownership(sk);
>        sock_put
>
> Add a receive queue cleanup in the socket destructor to fix this.
>
> syzkaller report:
>
> unreferenced object 0xffff8880117bfb80 (size 240):
>  comm "irq/56-vmw_vmci", pid 205, jiffies 4295064448 (age 73.992s)
>  hex dump (first 32 bytes):
>    78 dc 26 1e 80 88 ff ff 78 dc 26 1e 80 88 ff ff  x.&.....x.&.....
>    00 00 00 00 00 00 00 00 c0 da 26 1e 80 88 ff ff  ..........&.....
>  backtrace:
>    [<ffffffff82be8d97>] __alloc_skb+0x287/0x330 net/core/skbuff.c:505
>    [<ffffffffa114bcbd>] vmci_transport_recv_dgram_cb+0xbd/0x210 [vmw_vsock_vmci_transport]
>    [<ffffffffa05072c6>] vmci_datagram_invoke_guest_handler+0x366/0x450 [vmw_vmci]
>    [<ffffffffa050ad75>] vmci_dispatch_dgs+0x235/0x490 [vmw_vmci]
>    [<ffffffffa050b025>] vmci_interrupt+0x55/0x290 [vmw_vmci]
>    [<ffffffff8137ad2b>] irq_thread_fn+0x8b/0x1a0 kernel/irq/manage.c:1205
>    [<ffffffff8137c7ae>] irq_thread+0x28e/0x530 kernel/irq/manage.c:1314
>    [<ffffffff81253dd6>] kthread+0x2e6/0x3a0 kernel/kthread.c:376
>    [<ffffffff81004392>] ret_from_fork+0x22/0x30 arch/x86/entry/entry_64.S:295
>
> Found by InfoTeCS on behalf of Linux Verification Center
> (linuxtesting.org) with Syzkaller.
>
> Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
> Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov@xxxxxxxxxxx>
> ---
> net/vmw_vsock/af_vsock.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 9b71479a2b29..fbafd882a12c 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1048,6 +1048,7 @@ static void vsock_sk_destruct(struct sock *sk)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);

nit: maybe a comment here referring to vmci datagram could be nice to 
have if you send a v2. In any case, also this version is fine to me:

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

> +	__skb_queue_purge(&sk->sk_receive_queue);
> 	/* Flush MSG_ZEROCOPY leftovers. */
> 	__skb_queue_purge(&sk->sk_error_queue);
>
> --
> 2.47.3