Merge branch 'add-sock_kmemdup-helper'

Geliang Tang says:

====================
add sock_kmemdup helper

While developing MPTCP BPF path manager [1], I found it's useful to
add a new sock_kmemdup() helper.

My use case is this:

In mptcp_userspace_pm_append_new_local_addr() function (see patch 3
in this patchset), it uses sock_kmalloc() to allocate an address
entry "e", then immediately duplicate the input "entry" to it:

'''
	e = sock_kmalloc(sk, sizeof(*e), GFP_ATOMIC);
	if (!e) {
		ret = -ENOMEM;
		goto append_err;
	}

	*e = *entry;
'''

When I implemented MPTCP BPF path manager, I needed to implement a
code similar to this in BPF.

The kfunc sock_kmalloc() can be easily invoked in BPF to allocate
an entry "e", but the code "*e = *entry;" that assigns "entry" to
"e" is not easy to implemented.

I had to implement such a "copy entry" helper in BPF:

'''
static void mptcp_pm_copy_addr(struct mptcp_addr_info *dst,
                               struct mptcp_addr_info *src)
{
       dst->id = src->id;
       dst->family = src->family;
       dst->port = src->port;

       if (src->family == AF_INET) {
               dst->addr.s_addr = src->addr.s_addr;
       } else if (src->family == AF_INET6) {
               dst->addr6.s6_addr32[0] = src->addr6.s6_addr32[0];
               dst->addr6.s6_addr32[1] = src->addr6.s6_addr32[1];
               dst->addr6.s6_addr32[2] = src->addr6.s6_addr32[2];
               dst->addr6.s6_addr32[3] = src->addr6.s6_addr32[3];
       }
}

static void mptcp_pm_copy_entry(struct mptcp_pm_addr_entry *dst,
                                struct mptcp_pm_addr_entry *src)
{
       mptcp_pm_copy_addr(&dst->addr, &src->addr);

       dst->flags = src->flags;
       dst->ifindex = src->ifindex;
}
'''

And add "write permission" for BPF to each field of mptcp_pm_addr_entry:

'''
@@ static int bpf_mptcp_pm_btf_struct_access(struct bpf_verifier_log *log,
  case offsetof(struct mptcp_pm_addr_entry, addr.port):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.port);
    break;
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  case offsetof(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[0]):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[0]);
    break;
  case offsetof(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[1]):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[1]);
    break;
  case offsetof(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[2]):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[2]);
    break;
  case offsetof(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[3]):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.addr6.s6_addr32[3]);
    break;
 #else
  case offsetof(struct mptcp_pm_addr_entry, addr.addr.s_addr):
    end = offsetofend(struct mptcp_pm_addr_entry, addr.addr.s_addr);
    break;
 #endif
'''

But if there's a sock_kmemdup() helper, it will become much simpler,
only need to call kfunc sock_kmemdup() instead in BPF.

So this patchset adds this new helper and uses it in several places.

[1]
https://lore.kernel.org/mptcp/cover.1738924875.git.tanggeliang@kylinos.cn/
====================

Link: https://patch.msgid.link/cover.1740735165.git.tanggeliang@kylinos.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/sock.h

@@ -1797,6 +1797,8 @@ 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

@@ -2836,6 +2836,22 @@ void *sock_kmalloc(struct sock *sk, int size, gfp_t priority)
 }
 EXPORT_SYMBOL(sock_kmalloc);
 
+/*
+ * Duplicate the input "src" memory block using the socket's
+ * option memory buffer.
+ */
+void *sock_kmemdup(struct sock *sk, const void *src,
+		   int size, gfp_t priority)
+{
+	void *mem;
+
+	mem = sock_kmalloc(sk, size, priority);
+	if (mem)
+		memcpy(mem, src, size);
+	return mem;
+}
+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.

net/ipv6/exthdrs.c

@@ -1204,10 +1204,9 @@ ipv6_dup_options(struct sock *sk, struct ipv6_txoptions *opt)
 {
 	struct ipv6_txoptions *opt2;
 
-	opt2 = sock_kmalloc(sk, opt->tot_len, GFP_ATOMIC);
+	opt2 = sock_kmemdup(sk, opt, opt->tot_len, GFP_ATOMIC);
 	if (opt2) {
 		long dif = (char *)opt2 - (char *)opt;
-		memcpy(opt2, opt, opt->tot_len);
 		if (opt2->hopopt)
 			*((char **)&opt2->hopopt) += dif;
 		if (opt2->dst0opt)

net/mptcp/pm_userspace.c

@@ -71,13 +71,12 @@ static int mptcp_userspace_pm_append_new_local_addr(struct mptcp_sock *msk,
 		/* Memory for the entry is allocated from the
 		 * sock option buffer.
 		 */
-		e = sock_kmalloc(sk, sizeof(*e), GFP_ATOMIC);
+		e = sock_kmemdup(sk, entry, sizeof(*entry), GFP_ATOMIC);
 		if (!e) {
 			ret = -ENOMEM;
 			goto append_err;
 		}
 
-		*e = *entry;
 		if (!e->addr.id && needs_id)
 			e->addr.id = find_next_zero_bit(id_bitmap,
 							MPTCP_PM_MAX_ADDR_ID + 1,

net/mptcp/protocol.c

@@ -3178,12 +3178,9 @@ static void mptcp_copy_ip_options(struct sock *newsk, const struct sock *sk)
 	rcu_read_lock();
 	inet_opt = rcu_dereference(inet->inet_opt);
 	if (inet_opt) {
-		newopt = sock_kmalloc(newsk, sizeof(*inet_opt) +
+		newopt = sock_kmemdup(newsk, inet_opt, sizeof(*inet_opt) +
 				      inet_opt->opt.optlen, GFP_ATOMIC);
-		if (newopt)
-			memcpy(newopt, inet_opt, sizeof(*inet_opt) +
-			       inet_opt->opt.optlen);
-		else
+		if (!newopt)
 			net_warn_ratelimited("%s: Failed to copy ip options\n", __func__);
 	}
 	RCU_INIT_POINTER(newinet->inet_opt, newopt);

net/sctp/protocol.c

@@ -185,12 +185,9 @@ static void sctp_v4_copy_ip_options(struct sock *sk, struct sock *newsk)
 	rcu_read_lock();
 	inet_opt = rcu_dereference(inet->inet_opt);
 	if (inet_opt) {
-		newopt = sock_kmalloc(newsk, sizeof(*inet_opt) +
+		newopt = sock_kmemdup(newsk, inet_opt, sizeof(*inet_opt) +
 				      inet_opt->opt.optlen, GFP_ATOMIC);
-		if (newopt)
-			memcpy(newopt, inet_opt, sizeof(*inet_opt) +
-			       inet_opt->opt.optlen);
-		else
+		if (!newopt)
 			pr_err("%s: Failed to copy ip options\n", __func__);
 	}
 	RCU_INIT_POINTER(newinet->inet_opt, newopt);