[PATCH] ip_sockglue: Fix a missing-check bug in net/ipv4/ip_sockglue.c

[Gen Zhang <blackgod016574@gmail.com>]

In function ip_ra_control(), the pointer new_ra is allocated a memory 
space via kmalloc(). And it is used in the following codes. However, 
when  there is a memory allocation error, kmalloc() fails. Thus null 
pointer dereference may happen. And it will cause the kernel to crash. 
Therefore, we should check the return value and handle the error.

Signed-off-by: Gen Zhang <blackgod016574@gmail.com>

---
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 82f341e..d445839 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -343,6 +343,8 @@ int ip_ra_control(struct sock *sk, unsigned char on,
 		return -EINVAL;
 
 	new_ra = on ? kmalloc(sizeof(*new_ra), GFP_KERNEL) : NULL;
+	if (!new_ra)
+		return -ENOMEM;
 
 	mutex_lock(&net->ipv4.ra_mutex);
 	for (rap = &net->ipv4.ra_chain;