Subject: Re: [PATCH] net: Fix sock freeing before sock_init_data() with __sk_free()

From: Eric Dumazet <[email-masked]>
Date: Mon, 31 Aug 2009 08:26:43 +0200

Jarek Poplawski a écrit :
> After recent changes sk_free() frees socks conditionally and depends
> on sk_wmem_alloc beeing set e.g. in sock_init_data(). But in some
> cases sk_free() is called earlier, usually after other alloc errors.
> This patch fixes it by exporting and using __sk_free() directly.
> 
> Signed-off-by: Jarek Poplawski <[email-masked]>
> ---
> 
>  include/net/sock.h |    1 +
>  net/ax25/af_ax25.c |    6 +++---
>  net/core/sock.c    |    6 ++++--
>  net/irda/af_irda.c |    4 ++--
>  net/tipc/socket.c  |    2 +-
>  5 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 950409d..e76ef65 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -935,6 +935,7 @@ extern void release_sock(struct sock *sk);
>  extern struct sock		*sk_alloc(struct net *net, int family,
>  					  gfp_t priority,
>  					  struct proto *prot);
> +extern void			__sk_free(struct sock *sk);
>  extern void			sk_free(struct sock *sk);
>  extern void			sk_release_kernel(struct sock *sk);
>  extern struct sock		*sk_clone(const struct sock *sk,
> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
> index da0f64f..c05738c 100644
> --- a/net/ax25/af_ax25.c
> +++ b/net/ax25/af_ax25.c
> @@ -851,7 +851,7 @@ static int ax25_create(struct net *net, struct socket *sock, int protocol)
>  
>  	ax25 = sk->sk_protinfo = ax25_create_cb();
>  	if (!ax25) {
> -		sk_free(sk);
> +		__sk_free(sk);
>  		return -ENOMEM;
>  	}
>  
> @@ -876,7 +876,7 @@ struct sock *ax25_make_new(struct sock *osk, struct ax25_dev *ax25_dev)
>  		return NULL;
>  
>  	if ((ax25 = ax25_create_cb()) == NULL) {
> -		sk_free(sk);
> +		__sk_free(sk);
>  		return NULL;
>  	}
>  
> @@ -886,7 +886,7 @@ struct sock *ax25_make_new(struct sock *osk, struct ax25_dev *ax25_dev)
>  	case SOCK_SEQPACKET:
>  		break;
>  	default:
> -		sk_free(sk);
> +		__sk_free(sk);
>  		ax25_cb_put(ax25);
>  		return NULL;
>  	}
> diff --git a/net/core/sock.c b/net/core/sock.c
> index bbb25be..92793be 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1031,7 +1031,7 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
>  }
>  EXPORT_SYMBOL(sk_alloc);
>  
> -static void __sk_free(struct sock *sk)
> +void __sk_free(struct sock *sk)
>  {
>  	struct sk_filter *filter;
>  
> @@ -1054,13 +1054,15 @@ static void __sk_free(struct sock *sk)
>  	put_net(sock_net(sk));
>  	sk_prot_free(sk->sk_prot_creator, sk);
>  }
> +EXPORT_SYMBOL(__sk_free);
>  
>  void sk_free(struct sock *sk)
>  {
>  	/*
>  	 * We substract one from sk_wmem_alloc and can know if
>  	 * some packets are still in some tx queue.
> -	 * If not null, sock_wfree() will call __sk_free(sk) later
> +	 * If not null, sock_wfree() will call __sk_free(sk) later.
> +	 * (Before sock_init_data() etc. use __sk_free() instead.)
>  	 */
>  	if (atomic_dec_and_test(&sk->sk_wmem_alloc))
>  		__sk_free(sk);
> diff --git a/net/irda/af_irda.c b/net/irda/af_irda.c
> index 50b43c5..9ed2060 100644
> --- a/net/irda/af_irda.c
> +++ b/net/irda/af_irda.c
> @@ -1118,12 +1118,12 @@ static int irda_create(struct net *net, struct socket *sock, int protocol)
>  			self->max_sdu_size_rx = TTP_SAR_UNBOUND;
>  			break;
>  		default:
> -			sk_free(sk);
> +			__sk_free(sk);
>  			return -ESOCKTNOSUPPORT;
>  		}
>  		break;
>  	default:
> -		sk_free(sk);
> +		__sk_free(sk);
>  		return -ESOCKTNOSUPPORT;
>  	}
>  
> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> index 1848693..4c8435a 100644
> --- a/net/tipc/socket.c
> +++ b/net/tipc/socket.c
> @@ -228,7 +228,7 @@ static int tipc_create(struct net *net, struct socket *sock, int protocol)
>  	tp_ptr = tipc_createport_raw(sk, &dispatch, &wakeupdispatch,
>  				     TIPC_LOW_IMPORTANCE);
>  	if (unlikely(!tp_ptr)) {
> -		sk_free(sk);
> +		__sk_free(sk);
>  		return -ENOMEM;
>  	}
>  
> --

Very nice catch Jarek, but dont you think it would be cleaner to make sure
we can call sk_free() right after sk_alloc() instead, and not exporting
__sk_free() ?

ie initialize wmem_alloc in sk_alloc() instead of initializing it in 
sock_init_data() ?