[PATCH net-next v2 0/3] add sock_kmemdup helper

[Geliang Tang <geliang@kernel.org>]

From: Geliang Tang <tanggeliang@kylinos.cn>

v2:
 - add "EXPORT_SYMBOL(sock_kmemdup)" as Matthieu suggested.
 - drop the patch "use sock_kmemdup for tcp_ao_key".

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/

Geliang Tang (3):
  sock: add sock_kmemdup helper
  net: use sock_kmemdup for ip_options
  mptcp: use sock_kmemdup for address entry

 include/net/sock.h       |  2 ++
 net/core/sock.c          | 16 ++++++++++++++++
 net/ipv6/exthdrs.c       |  3 +--
 net/mptcp/pm_userspace.c |  3 +--
 net/mptcp/protocol.c     |  7 ++-----
 net/sctp/protocol.c      |  7 ++-----
 6 files changed, 24 insertions(+), 14 deletions(-)

-- 
2.43.0