[PATCH bpf-next] bpf, sockmap: Manual deletion of sockmap elements in user mode is not allowed

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---
 include/uapi/linux/bpf.h | 3 +++
 kernel/bpf/syscall.c     | 2 ++
 net/core/sock_map.c      | 3 +++
 3 files changed, 8 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4eebea830613..1dab090f271c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -1218,6 +1218,9 @@ enum {
 
 /* Create a map that is suitable to be an inner map with dynamic max entries */
 	BPF_F_INNER_MAP		= (1U << 12),
+
+/* This should only be used for bpf_map_delete_elem called by user. */
+	BPF_F_TCP_SOCKMAP	= (1U << 13),
 };
 
 /* Flags for BPF_PROG_QUERY. */

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index db402ebc5570..57aa98087322 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -1232,7 +1232,9 @@ static int map_delete_elem(union bpf_attr *attr)
 
 	bpf_disable_instrumentation();
 	rcu_read_lock();
+	map->map_flags |= BPF_F_TCP_SOCKMAP;
 	err = map->ops->map_delete_elem(map, key);
+	map->map_flags &= ~BPF_F_TCP_SOCKMAP;
 	rcu_read_unlock();
 	bpf_enable_instrumentation();
 	maybe_wait_bpf_programs(map);

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 2d213c4011db..5b90a35d1d23 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c

@@ -914,6 +914,9 @@ static int sock_hash_delete_elem(struct bpf_map *map, void *key)
 	struct bpf_shtab_elem *elem;
 	int ret = -ENOENT;
 
+	if (map->map_flags & BPF_F_TCP_SOCKMAP)
+		return -EOPNOTSUPP;
+
 	hash = sock_hash_bucket_hash(key, key_size);
 	bucket = sock_hash_select_bucket(htab, hash);
 

-- 
2.25.1

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

[...]

在 2022/3/14 23:30, Jakub Sitnicki 写道:

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

quoted

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

We use sk_msg to redirect with sock hash, like this:

  skA   redirect    skB
  Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
   sock_map_unref()
     sk_psock_put()
       sk_psock_drop()
         sk_psock_stop()
           __sk_psock_zap_ingress()
             __sk_psock_purge_ingress_msg()

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.


Thanks.

[...]
.

On Tue, Mar 15, 2022 at 03:24 PM +08, wangyufen wrote:

在 2022/3/14 23:30, Jakub Sitnicki 写道:

quoted

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

quoted

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

We use sk_msg to redirect with sock hash, like this:

 skA   redirect    skB
 Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
  sock_map_unref()
    sk_psock_put()
      sk_psock_drop()
        sk_psock_stop()
          __sk_psock_zap_ingress()
            __sk_psock_purge_ingress_msg()

quoted

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.

Thanks for the context. So, if I understand correctly, you want to avoid
breaking the network pipe by updating the sockmap from user-space.

This sounds awfully similar to BPF_MAP_FREEZE. Have you considered that?

On 3/15/22 1:12 PM, Jakub Sitnicki wrote:

On Tue, Mar 15, 2022 at 03:24 PM +08, wangyufen wrote:

quoted

在 2022/3/14 23:30, Jakub Sitnicki 写道:

quoted

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

quoted

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

We use sk_msg to redirect with sock hash, like this:

  skA   redirect    skB
  Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
   sock_map_unref()
     sk_psock_put()
       sk_psock_drop()
         sk_psock_stop()
           __sk_psock_zap_ingress()
             __sk_psock_purge_ingress_msg()

quoted

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.

Thanks for the context. So, if I understand correctly, you want to avoid
breaking the network pipe by updating the sockmap from user-space.

This sounds awfully similar to BPF_MAP_FREEZE. Have you considered that?

+1

Aside from that, the patch as-is also fails BPF CI in a lot of places, please
make sure to check selftests:

https://github.com/kernel-patches/bpf/runs/5537367301?check_suite_focus=true

   [...]
   #145/73 sockmap_listen/sockmap IPv6 test_udp_redir:OK
   #145/74 sockmap_listen/sockmap IPv6 test_udp_unix_redir:OK
   #145/75 sockmap_listen/sockmap Unix test_unix_redir:OK
   #145/76 sockmap_listen/sockmap Unix test_unix_redir:OK
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   #145/77 sockmap_listen/sockhash IPv4 TCP test_insert_invalid:FAIL
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   #145/78 sockmap_listen/sockhash IPv4 TCP test_insert_opened:FAIL
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   #145/79 sockmap_listen/sockhash IPv4 TCP test_insert_bound:FAIL
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   ./test_progs:test_ops_cleanup:1424: map_delete: expected EINVAL/ENOENT: Operation not supported
   test_ops_cleanup:FAIL:1424
   [...]

Thanks,
Daniel

On Tue, Mar 15, 2022 at 01:12:08PM +0100, Jakub Sitnicki wrote:

On Tue, Mar 15, 2022 at 03:24 PM +08, wangyufen wrote:

quoted

在 2022/3/14 23:30, Jakub Sitnicki 写道:

quoted

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

quoted

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

We use sk_msg to redirect with sock hash, like this:

 skA   redirect    skB
 Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
  sock_map_unref()
    sk_psock_put()
      sk_psock_drop()
        sk_psock_stop()
          __sk_psock_zap_ingress()
            __sk_psock_purge_ingress_msg()

quoted

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.

Thanks for the context. So, if I understand correctly, you want to avoid
breaking the network pipe by updating the sockmap from user-space.

This sounds awfully similar to BPF_MAP_FREEZE. Have you considered that?

Doesn't BPF_MAP_FREEZE only freeze write operations from syscalls?
For sockmap, receiving packets is not a part of map write operation.

The problem here is that skmsg can only be consumed when the socket is
still in the map, as it uses a separate queue and a separate type of
message (skmsg vs. skb). So, esstentially this behavior is by design.

Thanks.

在 2022/3/15 20:12, Jakub Sitnicki 写道:

On Tue, Mar 15, 2022 at 03:24 PM +08, wangyufen wrote:

quoted

在 2022/3/14 23:30, Jakub Sitnicki 写道:

quoted

On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:

quoted

A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
the sockmap element, the tcp socket will switch to use the TCP protocol
stack to send and receive packets. The switching process may cause some
issues, such as if some msgs exist in the ingress queue and are cleared
by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.

Signed-off-by: Wang Yufen <redacted>
---

Can you please tell us a bit more about the life-cycle of the socket in
your workload? Questions that come to mind:

1) What triggers the removal of the socket from sockmap in your case?

We use sk_msg to redirect with sock hash, like this:

  skA   redirect    skB
  Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
   sock_map_unref()
     sk_psock_put()
       sk_psock_drop()
         sk_psock_stop()
           __sk_psock_zap_ingress()
             __sk_psock_purge_ingress_msg()

quoted

2) Would it still be a problem if removal from sockmap did not cause any
packets to get dropped?

Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.

Thanks for the context. So, if I understand correctly, you want to avoid
breaking the network pipe by updating the sockmap from user-space.

This sounds awfully similar to BPF_MAP_FREEZE. Have you considered that?
.

Sorry, I didn't notice this. I used BPF_MAP_FREEZE to verify, can solve 
my problem, thanks.