sock: add sock_kmemdup helper

This patch adds the sock version of kmemdup() helper, named sock_kmemdup(),
to duplicate a memory block using the socket's option memory buffer.

Signed-off-by: Geliang Tang <[email protected]>

Author: Geliang Tang

include/net/sock.h

@@ -1793,6 +1793,7 @@ static inline struct sk_buff *sock_alloc_send_skb(struct sock *sk,
 }
 
 void *sock_kmalloc(struct sock *sk, int size, gfp_t priority);
+void *sock_kmemdup(struct sock *sk, const void *src, int size, gfp_t priority);
 void sock_kfree_s(struct sock *sk, void *mem, int size);
 void sock_kzfree_s(struct sock *sk, void *mem, int size);
 void sk_send_sigurg(struct sock *sk);

net/core/sock.c

@@ -2805,6 +2805,29 @@ void *sock_kmalloc(struct sock *sk, int size, gfp_t priority)
 }
 EXPORT_SYMBOL(sock_kmalloc);
 
+/*
+ * Duplicate a memory block using the socket's option memory buffer.
+ */
+void *sock_kmemdup(struct sock *sk, const void *src, int size, gfp_t priority)
+{
+	int optmem_max = READ_ONCE(sock_net(sk)->core.sysctl_optmem_max);
+
+	if ((unsigned int)size <= optmem_max &&
+	    atomic_read(&sk->sk_omem_alloc) + size < optmem_max) {
+		void *mem;
+		/* First do the add, to avoid the race if kmalloc
+		 * might sleep.
+		 */
+		atomic_add(size, &sk->sk_omem_alloc);
+		mem = kmemdup(src, size, priority);
+		if (mem)
+			return mem;
+		atomic_sub(size, &sk->sk_omem_alloc);
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(sock_kmemdup);
+
 /* Free an option memory block. Note, we actually want the inline
  * here as this allows gcc to detect the nullify and fold away the
  * condition entirely.