[PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen

[PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen

[Dudu Lu]

virtio_transport_recv_listen() calls sk_acceptq_added(sk) to increment
the listener's accept queue counter before calling
vsock_assign_transport(). When vsock_assign_transport() fails or selects
a different transport than the one that received the packet, the error
path returns without calling sk_acceptq_removed(sk), permanently
incrementing sk_ack_backlog.

A malicious VM peer can exploit this by sending repeated CONNECT
requests that trigger the transport mismatch condition. Each such
request permanently increments sk_ack_backlog. After approximately
backlog+1 such requests (default backlog ~128), sk_acceptq_is_full()
returns true, causing the listener to reject ALL new connections with
-ENOMEM. The only recovery is closing and re-creating the listener
socket.

Compare with vmci_transport.c and hyperv_transport.c which correctly
place sk_acceptq_added() AFTER the transport check, avoiding this
issue entirely.

Fix by moving sk_acceptq_added(sk) to after the transport validation
check, matching the pattern used by the other transports.

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Signed-off-by: Dudu Lu <phx0fer@gmail.com>
---
 net/vmw_vsock/virtio_transport_common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 8a9fb23c6e85..29e1d9833be4 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1,3 +1,4 @@
+	sk_acceptq_added(sk);
 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * common code for virtio vsock
@@ -1560,8 +1561,9 @@ virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb,
 		return -ENOMEM;
 	}
 
-	sk_acceptq_added(sk);
 
+
+	sk_acceptq_added(sk);
 	lock_sock_nested(child, SINGLE_DEPTH_NESTING);
 
 	child->sk_state = TCP_ESTABLISHED;
-- 
2.39.3 (Apple Git-145)

Re: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen

[Stefano Garzarella]

On Mon, Apr 13, 2026 at 04:52:43PM +0800, Dudu Lu wrote:
>virtio_transport_recv_listen() calls sk_acceptq_added(sk) to increment
>the listener's accept queue counter before calling
>vsock_assign_transport(). When vsock_assign_transport() fails or selects
>a different transport than the one that received the packet, the error
>path returns without calling sk_acceptq_removed(sk), permanently
>incrementing sk_ack_backlog.
>
>A malicious VM peer can exploit this by sending repeated CONNECT
>requests that trigger the transport mismatch condition. Each such
>request permanently increments sk_ack_backlog. After approximately
>backlog+1 such requests (default backlog ~128), sk_acceptq_is_full()
>returns true, causing the listener to reject ALL new connections with
>-ENOMEM. The only recovery is closing and re-creating the listener
>socket.
>
>Compare with vmci_transport.c and hyperv_transport.c which correctly
>place sk_acceptq_added() AFTER the transport check, avoiding this
>issue entirely.
>
>Fix by moving sk_acceptq_added(sk) to after the transport validation
>check, matching the pattern used by the other transports.

The issue seems legitimate, but this patch doesn't do what you're 
describing here.

Out of curiosity, how did you generate it?

Stefano


>
>Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
>Signed-off-by: Dudu Lu <phx0fer@gmail.com>
>---
> net/vmw_vsock/virtio_transport_common.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 8a9fb23c6e85..29e1d9833be4 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1,3 +1,4 @@
>+	sk_acceptq_added(sk);
> // SPDX-License-Identifier: GPL-2.0-only
> /*
>  * common code for virtio vsock
>@@ -1560,8 +1561,9 @@ virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb,
> 		return -ENOMEM;
> 	}
>
>-	sk_acceptq_added(sk);
>
>+
>+	sk_acceptq_added(sk);
> 	lock_sock_nested(child, SINGLE_DEPTH_NESTING);
>
> 	child->sk_state = TCP_ESTABLISHED;
>-- 
>2.39.3 (Apple Git-145)
>

Re: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen

[kernel test robot]

Hi Dudu,

kernel test robot noticed the following build errors:

[auto build test ERROR on mst-vhost/linux-next]
[also build test ERROR on net/main net-next/main linus/master horms-ipvs/master v7.0 next-20260414]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dudu-Lu/vsock-virtio-fix-accept-queue-count-leak-on-transport-mismatch-in-recv_listen/20260414-233232
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link:    https://lore.kernel.org/r/20260413085243.73200-1-phx0fer%40gmail.com
patch subject: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen
config: sparc-randconfig-001-20260415 (https://download.01.org/0day-ci/archive/20260415/202604150747.6LyaJckM-lkp@intel.com/config)
compiler: sparc64-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260415/202604150747.6LyaJckM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604150747.6LyaJckM-lkp@intel.com/

All errors (new ones prefixed by >>):

   net/vmw_vsock/virtio_transport_common.c:1:2: warning: data definition has no type or storage class
     sk_acceptq_added(sk);
     ^~~~~~~~~~~~~~~~
   net/vmw_vsock/virtio_transport_common.c:1:2: error: type defaults to 'int' in declaration of 'sk_acceptq_added' [-Werror=implicit-int]
   net/vmw_vsock/virtio_transport_common.c:1:2: warning: parameter names (without types) in function declaration
   In file included from include/linux/virtio_vsock.h:7,
                    from net/vmw_vsock/virtio_transport_common.c:15:
>> include/net/sock.h:1080:20: error: conflicting types for 'sk_acceptq_added'
    static inline void sk_acceptq_added(struct sock *sk)
                       ^~~~~~~~~~~~~~~~
   net/vmw_vsock/virtio_transport_common.c:1:2: note: previous declaration of 'sk_acceptq_added' was here
     sk_acceptq_added(sk);
     ^~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +/sk_acceptq_added +1080 include/net/sock.h

^1da177e4c3f415 Linus Torvalds 2005-04-16  1079  
^1da177e4c3f415 Linus Torvalds 2005-04-16 @1080  static inline void sk_acceptq_added(struct sock *sk)
^1da177e4c3f415 Linus Torvalds 2005-04-16  1081  {
288efe8606b62d0 Eric Dumazet   2019-11-05  1082  	WRITE_ONCE(sk->sk_ack_backlog, sk->sk_ack_backlog + 1);
^1da177e4c3f415 Linus Torvalds 2005-04-16  1083  }
^1da177e4c3f415 Linus Torvalds 2005-04-16  1084  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen

[kernel test robot]

Hi Dudu,

kernel test robot noticed the following build errors:

[auto build test ERROR on mst-vhost/linux-next]
[also build test ERROR on net/main net-next/main linus/master horms-ipvs/master v7.0 next-20260414]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dudu-Lu/vsock-virtio-fix-accept-queue-count-leak-on-transport-mismatch-in-recv_listen/20260414-233232
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link:    https://lore.kernel.org/r/20260413085243.73200-1-phx0fer%40gmail.com
patch subject: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen
config: arc-randconfig-001-20260415 (https://download.01.org/0day-ci/archive/20260415/202604150741.iQBI3cGE-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 13.4.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260415/202604150741.iQBI3cGE-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604150741.iQBI3cGE-lkp@intel.com/

All error/warnings (new ones prefixed by >>):

>> net/vmw_vsock/virtio_transport_common.c:1:9: warning: data definition has no type or storage class
       1 |         sk_acceptq_added(sk);
         |         ^~~~~~~~~~~~~~~~
>> net/vmw_vsock/virtio_transport_common.c:1:9: error: type defaults to 'int' in declaration of 'sk_acceptq_added' [-Werror=implicit-int]
>> net/vmw_vsock/virtio_transport_common.c:1:9: warning: parameter names (without types) in function declaration
   In file included from include/linux/virtio_vsock.h:7,
                    from net/vmw_vsock/virtio_transport_common.c:15:
>> include/net/sock.h:1080:20: error: conflicting types for 'sk_acceptq_added'; have 'void(struct sock *)'
    1080 | static inline void sk_acceptq_added(struct sock *sk)
         |                    ^~~~~~~~~~~~~~~~
   net/vmw_vsock/virtio_transport_common.c:1:9: note: previous declaration of 'sk_acceptq_added' with type 'int()'
       1 |         sk_acceptq_added(sk);
         |         ^~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +1 net/vmw_vsock/virtio_transport_common.c

   > 1		sk_acceptq_added(sk);
     2	// SPDX-License-Identifier: GPL-2.0-only
     3	/*
     4	 * common code for virtio vsock
     5	 *
     6	 * Copyright (C) 2013-2015 Red Hat, Inc.
     7	 * Author: Asias He <asias@redhat.com>
     8	 *         Stefan Hajnoczi <stefanha@redhat.com>
     9	 */
    10	#include <linux/spinlock.h>
    11	#include <linux/module.h>
    12	#include <linux/sched/signal.h>
    13	#include <linux/ctype.h>
    14	#include <linux/list.h>
    15	#include <linux/virtio_vsock.h>
    16	#include <uapi/linux/vsockmon.h>
    17	

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