From: luoqing <luoqing@kylinos.cn>

The 'err' parameter in sctp_skb_recv_datagram() is never used by any
of its callers. Both sctp_recvmsg() and sctp_ulpevent_read_nxtinfo()
pass the address of a local variable but never check its value after
the function returns, rendering the parameter completely useless.

Remove the unused parameter to simplify the function signature and
eliminate dead code.

Signed-off-by: luoqing <luoqing@kylinos.cn>
---
 include/net/sctp/sctp.h |  2 +-
 net/sctp/socket.c       | 10 +++-------
 net/sctp/ulpevent.c     |  3 +--
 3 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index d50c27812504..b86d50d6b146 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);
 
 extern struct percpu_counter sctp_sockets_allocated;
 int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
-struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);
 
 typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);
 void sctp_transport_walk_start(struct rhashtable_iter *iter);
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c7b9e325ec1c..3804382d78e0 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2123,7 +2123,7 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		goto out;
 	}
 
-	skb = sctp_skb_recv_datagram(sk, flags, &err);
+	skb = sctp_skb_recv_datagram(sk, flags);
 	if (!skb)
 		goto out;
 
@@ -9082,7 +9082,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)
  * Note: This is pretty much the same routine as in core/datagram.c
  * with a few changes to make lksctp work.
  */
-struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)
 {
 	int error;
 	struct sk_buff *skb;
@@ -9120,17 +9120,13 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
 		if (sk->sk_shutdown & RCV_SHUTDOWN)
 			break;
 
-
 		/* User doesn't want to wait.  */
 		error = -EAGAIN;
 		if (!timeo)
 			goto no_packet;
-	} while (sctp_wait_for_packet(sk, err, &timeo) == 0);
-
-	return NULL;
+	} while (sctp_wait_for_packet(sk, &error, &timeo) == 0);
 
 no_packet:
-	*err = error;
 	return NULL;
 }
 
diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index 8920ca92a011..8ed51a15c3a4 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -1061,9 +1061,8 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
 				struct sock *sk)
 {
 	struct sk_buff *skb;
-	int err;
 
-	skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, &err);
+	skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);
 	if (skb != NULL) {
 		__sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
 					     msghdr, skb);
-- 
2.25.1

On Fri, Jul 17, 2026 at 4:21 AM luoqing <l1138897701@163.com> wrote:
>
> From: luoqing <luoqing@kylinos.cn>
>
> The 'err' parameter in sctp_skb_recv_datagram() is never used by any
> of its callers. Both sctp_recvmsg() and sctp_ulpevent_read_nxtinfo()
> pass the address of a local variable but never check its value after
> the function returns, rendering the parameter completely useless.
>
> Remove the unused parameter to simplify the function signature and
> eliminate dead code.
>
> Signed-off-by: luoqing <luoqing@kylinos.cn>
> ---
>  include/net/sctp/sctp.h |  2 +-
>  net/sctp/socket.c       | 10 +++-------
>  net/sctp/ulpevent.c     |  3 +--
>  3 files changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index d50c27812504..b86d50d6b146 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);
>
>  extern struct percpu_counter sctp_sockets_allocated;
>  int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
> -struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
> +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);
>
>  typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);
>  void sctp_transport_walk_start(struct rhashtable_iter *iter);
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index c7b9e325ec1c..3804382d78e0 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -2123,7 +2123,7 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
>                 goto out;
>         }
>
> -       skb = sctp_skb_recv_datagram(sk, flags, &err);
> +       skb = sctp_skb_recv_datagram(sk, flags);
>         if (!skb)
>                 goto out;
>
> @@ -9082,7 +9082,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)
>   * Note: This is pretty much the same routine as in core/datagram.c
>   * with a few changes to make lksctp work.
>   */
> -struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
> +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)
>  {
>         int error;
>         struct sk_buff *skb;
> @@ -9120,17 +9120,13 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
>                 if (sk->sk_shutdown & RCV_SHUTDOWN)
>                         break;
>
> -
>                 /* User doesn't want to wait.  */
>                 error = -EAGAIN;
>                 if (!timeo)
>                         goto no_packet;
> -       } while (sctp_wait_for_packet(sk, err, &timeo) == 0);
> -
> -       return NULL;
> +       } while (sctp_wait_for_packet(sk, &error, &timeo) == 0);
>
>  no_packet:
> -       *err = error;
>         return NULL;
>  }
>
> diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
> index 8920ca92a011..8ed51a15c3a4 100644
> --- a/net/sctp/ulpevent.c
> +++ b/net/sctp/ulpevent.c
> @@ -1061,9 +1061,8 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
>                                 struct sock *sk)
>  {
>         struct sk_buff *skb;
> -       int err;
>
> -       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, &err);
> +       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);
>         if (skb != NULL) {
>                 __sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
>                                              msghdr, skb);
> --
> 2.25.1
>
I think it's used at [1] in sctp_recvmsg():

        skb = sctp_skb_recv_datagram(sk, flags, &err);
        if (!skb)
                goto out;
...

out:
        release_sock(sk);
        return err;   <------ [1]

Thanks.

On Fri, 17 Jul 2026 11:10:21 -0400
Xin Long <lucien.xin@gmail.com> wrote:

> On Fri, Jul 17, 2026 at 4:21 AM luoqing <l1138897701@163.com> wrote:
> >
> > From: luoqing <luoqing@kylinos.cn>
> >
> > The 'err' parameter in sctp_skb_recv_datagram() is never used by any
> > of its callers. Both sctp_recvmsg() and sctp_ulpevent_read_nxtinfo()
> > pass the address of a local variable but never check its value after
> > the function returns, rendering the parameter completely useless.
> >
> > Remove the unused parameter to simplify the function signature and
> > eliminate dead code.
> >
> > Signed-off-by: luoqing <luoqing@kylinos.cn>
> > ---
> >  include/net/sctp/sctp.h |  2 +-
> >  net/sctp/socket.c       | 10 +++-------
> >  net/sctp/ulpevent.c     |  3 +--
> >  3 files changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> > index d50c27812504..b86d50d6b146 100644
> > --- a/include/net/sctp/sctp.h
> > +++ b/include/net/sctp/sctp.h
> > @@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);
> >
> >  extern struct percpu_counter sctp_sockets_allocated;
> >  int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
> > -struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
> > +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);
> >
> >  typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);
> >  void sctp_transport_walk_start(struct rhashtable_iter *iter);
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index c7b9e325ec1c..3804382d78e0 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -2123,7 +2123,7 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
> >                 goto out;
> >         }
> >
> > -       skb = sctp_skb_recv_datagram(sk, flags, &err);
> > +       skb = sctp_skb_recv_datagram(sk, flags);
> >         if (!skb)
> >                 goto out;
> >
> > @@ -9082,7 +9082,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)
> >   * Note: This is pretty much the same routine as in core/datagram.c
> >   * with a few changes to make lksctp work.
> >   */
> > -struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
> > +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)
> >  {
> >         int error;
> >         struct sk_buff *skb;
> > @@ -9120,17 +9120,13 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
> >                 if (sk->sk_shutdown & RCV_SHUTDOWN)
> >                         break;
> >
> > -
> >                 /* User doesn't want to wait.  */
> >                 error = -EAGAIN;
> >                 if (!timeo)
> >                         goto no_packet;
> > -       } while (sctp_wait_for_packet(sk, err, &timeo) == 0);
> > -
> > -       return NULL;
> > +       } while (sctp_wait_for_packet(sk, &error, &timeo) == 0);
> >
> >  no_packet:
> > -       *err = error;
> >         return NULL;
> >  }
> >
> > diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
> > index 8920ca92a011..8ed51a15c3a4 100644
> > --- a/net/sctp/ulpevent.c
> > +++ b/net/sctp/ulpevent.c
> > @@ -1061,9 +1061,8 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
> >                                 struct sock *sk)
> >  {
> >         struct sk_buff *skb;
> > -       int err;
> >
> > -       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, &err);
> > +       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);
> >         if (skb != NULL) {
> >                 __sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
> >                                              msghdr, skb);
> > --
> > 2.25.1
> >  
> I think it's used at [1] in sctp_recvmsg():
> 
>         skb = sctp_skb_recv_datagram(sk, flags, &err);
>         if (!skb)
>                 goto out;

Would it make more sense to ERR_PTR() etc ?

	David

> ...
> 
> out:
>         release_sock(sk);
>         return err;   <------ [1]
> 
> Thanks.
> 

On Fri, Jul 17, 2026 at 2:19 PM David Laight
<david.laight.linux@gmail.com> wrote:
>
> On Fri, 17 Jul 2026 11:10:21 -0400
> Xin Long <lucien.xin@gmail.com> wrote:
>
> > On Fri, Jul 17, 2026 at 4:21 AM luoqing <l1138897701@163.com> wrote:
> > >
> > > From: luoqing <luoqing@kylinos.cn>
> > >
> > > The 'err' parameter in sctp_skb_recv_datagram() is never used by any
> > > of its callers. Both sctp_recvmsg() and sctp_ulpevent_read_nxtinfo()
> > > pass the address of a local variable but never check its value after
> > > the function returns, rendering the parameter completely useless.
> > >
> > > Remove the unused parameter to simplify the function signature and
> > > eliminate dead code.
> > >
> > > Signed-off-by: luoqing <luoqing@kylinos.cn>
> > > ---
> > >  include/net/sctp/sctp.h |  2 +-
> > >  net/sctp/socket.c       | 10 +++-------
> > >  net/sctp/ulpevent.c     |  3 +--
> > >  3 files changed, 5 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> > > index d50c27812504..b86d50d6b146 100644
> > > --- a/include/net/sctp/sctp.h
> > > +++ b/include/net/sctp/sctp.h
> > > @@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);
> > >
> > >  extern struct percpu_counter sctp_sockets_allocated;
> > >  int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
> > > -struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
> > > +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);
> > >
> > >  typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);
> > >  void sctp_transport_walk_start(struct rhashtable_iter *iter);
> > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > index c7b9e325ec1c..3804382d78e0 100644
> > > --- a/net/sctp/socket.c
> > > +++ b/net/sctp/socket.c
> > > @@ -2123,7 +2123,7 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
> > >                 goto out;
> > >         }
> > >
> > > -       skb = sctp_skb_recv_datagram(sk, flags, &err);
> > > +       skb = sctp_skb_recv_datagram(sk, flags);
> > >         if (!skb)
> > >                 goto out;
> > >
> > > @@ -9082,7 +9082,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)
> > >   * Note: This is pretty much the same routine as in core/datagram.c
> > >   * with a few changes to make lksctp work.
> > >   */
> > > -struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
> > > +struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)
> > >  {
> > >         int error;
> > >         struct sk_buff *skb;
> > > @@ -9120,17 +9120,13 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
> > >                 if (sk->sk_shutdown & RCV_SHUTDOWN)
> > >                         break;
> > >
> > > -
> > >                 /* User doesn't want to wait.  */
> > >                 error = -EAGAIN;
> > >                 if (!timeo)
> > >                         goto no_packet;
> > > -       } while (sctp_wait_for_packet(sk, err, &timeo) == 0);
> > > -
> > > -       return NULL;
> > > +       } while (sctp_wait_for_packet(sk, &error, &timeo) == 0);
> > >
> > >  no_packet:
> > > -       *err = error;
> > >         return NULL;
> > >  }
> > >
> > > diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
> > > index 8920ca92a011..8ed51a15c3a4 100644
> > > --- a/net/sctp/ulpevent.c
> > > +++ b/net/sctp/ulpevent.c
> > > @@ -1061,9 +1061,8 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
> > >                                 struct sock *sk)
> > >  {
> > >         struct sk_buff *skb;
> > > -       int err;
> > >
> > > -       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, &err);
> > > +       skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);
> > >         if (skb != NULL) {
> > >                 __sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
> > >                                              msghdr, skb);
> > > --
> > > 2.25.1
> > >
> > I think it's used at [1] in sctp_recvmsg():
> >
> >         skb = sctp_skb_recv_datagram(sk, flags, &err);
> >         if (!skb)
> >                 goto out;
>
> Would it make more sense to ERR_PTR() etc ?
>
Let's keep consistent with skb_recv_datagram() where it's &err,
besides, there's a shutdown condition (returns 0 via err param).

Thanks.