net: selectively purge error queue in IP_RECVERR / IPV6_RECVERR

Setting IP_RECVERR and IPV6_RECVERR options to zero currently
purges the socket error queue, which was probably not expected
for zerocopy and tx_timestamp users.

I discovered this issue while preparing commit 6b5f43ea
("inet: move inet->recverr to inet->inet_flags"), I presume this
change does not need to be backported to stable kernels.

Add skb_errqueue_purge() helper to purge error messages only.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -3180,6 +3180,7 @@ static inline void skb_queue_purge(struct sk_buff_head *list)
 }
 
 unsigned int skb_rbtree_purge(struct rb_root *root);
+void skb_errqueue_purge(struct sk_buff_head *list);
 
 void *__netdev_alloc_frag_align(unsigned int fragsz, unsigned int align_mask);
 

net/core/skbuff.c

@@ -3745,6 +3745,27 @@ unsigned int skb_rbtree_purge(struct rb_root *root)
 	return sum;
 }
 
+void skb_errqueue_purge(struct sk_buff_head *list)
+{
+	struct sk_buff *skb, *next;
+	struct sk_buff_head kill;
+	unsigned long flags;
+
+	__skb_queue_head_init(&kill);
+
+	spin_lock_irqsave(&list->lock, flags);
+	skb_queue_walk_safe(list, skb, next) {
+		if (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY ||
+		    SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_TIMESTAMPING)
+			continue;
+		__skb_unlink(skb, list);
+		__skb_queue_tail(&kill, skb);
+	}
+	spin_unlock_irqrestore(&list->lock, flags);
+	__skb_queue_purge(&kill);
+}
+EXPORT_SYMBOL(skb_errqueue_purge);
+
 /**
  *	skb_queue_head - queue a buffer at the list head
  *	@list: list to use

net/ipv4/ip_sockglue.c

@@ -976,7 +976,7 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 	case IP_RECVERR:
 		inet_assign_bit(RECVERR, sk, val);
 		if (!val)
-			skb_queue_purge(&sk->sk_error_queue);
+			skb_errqueue_purge(&sk->sk_error_queue);
 		return 0;
 	case IP_RECVERR_RFC4884:
 		if (val < 0 || val > 1)

net/ipv6/ipv6_sockglue.c

@@ -923,7 +923,7 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 			goto e_inval;
 		np->recverr = valbool;
 		if (!val)
-			skb_queue_purge(&sk->sk_error_queue);
+			skb_errqueue_purge(&sk->sk_error_queue);
 		retv = 0;
 		break;
 	case IPV6_FLOWINFO_SEND: