ipv6: Don't depend on per socket memory for neighbour discovery messages

[ Upstream commit 25a6e6b8 ]

Allocating skbs when sending out neighbour discovery messages
currently uses sock_alloc_send_skb() based on a per net namespace
socket and thus share a socket wmem buffer space.

If a netdevice is temporarily unable to transmit due to carrier
loss or for other reasons, the queued up ndisc messages will cosnume
all of the wmem space and will thus prevent from any more skbs to
be allocated even for netdevices that are able to transmit packets.

The number of neighbour discovery messages sent is very limited,
use of alloc_skb() bypasses the socket wmem buffer size enforcement
while the manual call to skb_set_owner_w() maintains the socket
reference needed for the IPv6 output path.

This patch has orginally been posted by Eric Dumazet in a modified
form.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Fabio Estevam <festevam@gmail.com>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/ipv6/ndisc.c

@@ -449,7 +449,6 @@ struct sk_buff *ndisc_build_skb(struct net_device *dev,
 	struct sk_buff *skb;
 	struct icmp6hdr *hdr;
 	int len;
-	int err;
 	u8 *opt;
 
 	if (!dev->addr_len)
@@ -459,14 +458,12 @@ struct sk_buff *ndisc_build_skb(struct net_device *dev,
 	if (llinfo)
 		len += ndisc_opt_addr_space(dev);
 
-	skb = sock_alloc_send_skb(sk,
-				  (MAX_HEADER + sizeof(struct ipv6hdr) +
-				   len + LL_ALLOCATED_SPACE(dev)),
-				  1, &err);
+	skb = alloc_skb((MAX_HEADER + sizeof(struct ipv6hdr) +
+			 len + LL_ALLOCATED_SPACE(dev)), GFP_ATOMIC);
 	if (!skb) {
 		ND_PRINTK0(KERN_ERR
-			   "ICMPv6 ND: %s() failed to allocate an skb, err=%d.\n",
-			   __func__, err);
+			   "ICMPv6 ND: %s() failed to allocate an skb.\n",
+			   __func__);
 		return NULL;
 	}
 
@@ -494,6 +491,11 @@ struct sk_buff *ndisc_build_skb(struct net_device *dev,
 					   csum_partial(hdr,
 							len, 0));
 
+	/* Manually assign socket ownership as we avoid calling
+	 * sock_alloc_send_pskb() to bypass wmem buffer limits
+	 */
+	skb_set_owner_w(skb, sk);
+
 	return skb;
 }