2023-07-04 11:14:21

by Wang Ming

Subject: [PATCH v1] fs:dlm:Fix NULL pointer dereference bug in accept_from_sock()

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 <[email protected]>
---
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

2023-07-04 16:37:34

by Alexander Aring

Subject: Re: [Cluster-devel] [PATCH v1] fs:dlm:Fix NULL pointer dereference bug in accept_from_sock()

Hi,

On Tue, Jul 4, 2023 at 6:56 AM Wang Ming <[email protected]> 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 <[email protected]>
> ---
> 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