[net] udp: properly cope with csum errors

From: Eric Dumazet <edumazet@google.com>

Dmitry reported that UDP sockets being destroyed would trigger the
WARN_ON(atomic_read(&sk->sk_rmem_alloc)); in inet_sock_destruct()

It turns out we do not properly destroy skb(s) that have wrong UDP
checksum.

Thanks again to syzkaller team.

Fixes : 7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
---
 include/net/sock.h  |    4 +++-
 net/core/datagram.c |    8 ++++++--
 net/ipv4/udp.c      |    2 +-
 net/ipv6/udp.c      |    2 +-
 4 files changed, 11 insertions(+), 5 deletions(-)

On Sun, 2017-02-05 at 09:25 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Dmitry reported that UDP sockets being destroyed would trigger the
> WARN_ON(atomic_read(&sk->sk_rmem_alloc)); in inet_sock_destruct()
> 
> It turns out we do not properly destroy skb(s) that have wrong UDP
> checksum.
> 
> Thanks again to syzkaller team.
> 
> Fixes : 7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
> ---
>  include/net/sock.h  |    4 +++-
>  net/core/datagram.c |    8 ++++++--
>  net/ipv4/udp.c      |    2 +-
>  net/ipv6/udp.c      |    2 +-
>  4 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index f0e867f58722..c4f5e6fca17c 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2006,7 +2006,9 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
>  void sk_stop_timer(struct sock *sk, struct timer_list *timer);
>  
>  int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
> -			unsigned int flags);
> +			unsigned int flags,
> +			void (*destructor)(struct sock *sk,
> +					   struct sk_buff *skb));
>  int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
>  int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
>  
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index 662bea587165..ea633342ab0d 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -332,7 +332,9 @@ void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
>  EXPORT_SYMBOL(__skb_free_datagram_locked);
>  
>  int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
> -			unsigned int flags)
> +			unsigned int flags,
> +			void (*destructor)(struct sock *sk,
> +					   struct sk_buff *skb))
>  {
>  	int err = 0;
>  
> @@ -342,6 +344,8 @@ int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
>  		if (skb == skb_peek(&sk->sk_receive_queue)) {
>  			__skb_unlink(skb, &sk->sk_receive_queue);
>  			atomic_dec(&skb->users);
> +			if (destructor)
> +				destructor(sk, skb);
>  			err = 0;
>  		}
>  		spin_unlock_bh(&sk->sk_receive_queue.lock);
> @@ -375,7 +379,7 @@ EXPORT_SYMBOL(__sk_queue_drop_skb);
>  
>  int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
>  {
> -	int err = __sk_queue_drop_skb(sk, skb, flags);
> +	int err = __sk_queue_drop_skb(sk, skb, flags, NULL);
>  
>  	kfree_skb(skb);
>  	sk_mem_reclaim_partial(sk);
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 1307a7c2e544..8aab7d78d25b 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1501,7 +1501,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
>  	return err;
>  
>  csum_copy_err:
> -	if (!__sk_queue_drop_skb(sk, skb, flags)) {
> +	if (!__sk_queue_drop_skb(sk, skb, flags, udp_skb_destructor)) {
>  		UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
>  		UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
>  	}
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 4d5c4eee4b3f..8990856f5101 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -441,7 +441,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
>  	return err;
>  
>  csum_copy_err:
> -	if (!__sk_queue_drop_skb(sk, skb, flags)) {
> +	if (!__sk_queue_drop_skb(sk, skb, flags, udp_skb_destructor)) {
>  		if (is_udp4) {
>  			UDP_INC_STATS(sock_net(sk),
>  				      UDP_MIB_CSUMERRORS, is_udplite);


LGTM, Thanks Eric for fixing this!

Acked-by: Paolo Abeni <pabeni@redhat.com>