newcon -> sock is NULL but dereferenced.
First check newcon. Whether sock is a null pointer.
If so, the subsequent operations are skipped.
If it is not empty, perform subsequent operations.

Signed-off-by: Wang Ming <machel@vivo.com>
---
 fs/dlm/lowcomms.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 9f14ea9f6..ea18b9478 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -1081,9 +1081,12 @@ static int accept_from_sock(void)
 		add_sock(newsock, newcon);
 
 		/* check if we receved something while adding */
-		lock_sock(newcon->sock->sk);
-		lowcomms_queue_rwork(newcon);
-		release_sock(newcon->sock->sk);
+		if (newcon->sock) {
+			lock_sock(newcon->sock->sk);
+			lowcomms_queue_rwork(newcon);
+			release_sock(newcon->sock->sk);
+		}
+
 	}
 	up_write(&newcon->sock_lock);
 	srcu_read_unlock(&connections_srcu, idx);
-- 
2.25.1

Hi,

On Tue, Jul 4, 2023 at 6:56 AM Wang Ming <machel@vivo.com> wrote:
>
> newcon -> sock is NULL but dereferenced.
> First check newcon. Whether sock is a null pointer.
> If so, the subsequent operations are skipped.
> If it is not empty, perform subsequent operations.
>

did you experience some null pointer dereference? If so, on which kernel was it?

> Signed-off-by: Wang Ming <machel@vivo.com>
> ---
>  fs/dlm/lowcomms.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
> index 9f14ea9f6..ea18b9478 100644
> --- a/fs/dlm/lowcomms.c
> +++ b/fs/dlm/lowcomms.c
> @@ -1081,9 +1081,12 @@ static int accept_from_sock(void)
>                 add_sock(newsock, newcon);
>

Here in add_sock() we assign newcon->sock = newsock. It cannot fail
and newsock cannot be null, so holding the newcon->sock_lock write
protected _should_ be safe that others don't manipulate newcon->sock.
It should, that's why I am asking if you experienced some issue here?

>                 /* check if we receved something while adding */
> -               lock_sock(newcon->sock->sk);
> -               lowcomms_queue_rwork(newcon);
> -               release_sock(newcon->sock->sk);

see above, newcon->sock should always be set at this point.

> +               if (newcon->sock) {
> +                       lock_sock(newcon->sock->sk);
> +                       lowcomms_queue_rwork(newcon);
> +                       release_sock(newcon->sock->sk);
> +               }
> +
>         }
>         up_write(&newcon->sock_lock);
>         srcu_read_unlock(&connections_srcu, idx);

- Alex