net: mctp: use nlmsg_payload() for netlink message data extraction

Jakub suggests:

> I have a different request :) Matt, once this ends up in net-next
> (end of this week) could you refactor it to use nlmsg_payload() ?
> It doesn't exist in net but this is exactly why it was added.

This refactors the additions to both mctp_dump_addrinfo(), and
mctp_rtm_getneigh() - two cases where we're calling nlh_data() on an
an incoming netlink message, without a prior nlmsg_parse().

For the neigh.c case, we cannot hit the failure where the nlh does not
contain a full ndmsg at present, as the core handler
(net/core/neighbour.c, neigh_get()) has already validated the size
through neigh_valid_req_get(), and would have failed the get operation
before the MCTP hander is called.

However, relying on that is a bit fragile, so apply the nlmsg_payload
refector here too.

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20250521-mctp-nlmsg-payload-v2-1-e85df160c405@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/mctp/device.c b/net/mctp/device.c
index 7c0dcf3df3196207af6e1a1c002f388265c49fa1..4d404edd7446e187dd3aa18ee2086c4e2e3da3ee 100644 (file)
--- a/net/mctp/device.c
+++ b/net/mctp/device.c
@@ -120,8 +120,8 @@ static int mctp_dump_addrinfo(struct sk_buff *skb, struct netlink_callback *cb)
        int ifindex = 0, rc;
 
        /* Filter by ifindex if a header is provided */
-       if (cb->nlh->nlmsg_len >= nlmsg_msg_size(sizeof(*hdr))) {
-               hdr = nlmsg_data(cb->nlh);
+       hdr = nlmsg_payload(cb->nlh, sizeof(*hdr));
+       if (hdr) {
                ifindex = hdr->ifa_index;
        } else {
                if (cb->strict_check) {

diff --git a/net/mctp/neigh.c b/net/mctp/neigh.c
index 590f642413e4ef113a1a9fa96cb548b98cb55621..05b899f22d902b275ca1e300542a8d546d59ea15 100644 (file)
--- a/net/mctp/neigh.c
+++ b/net/mctp/neigh.c
@@ -250,7 +250,10 @@ static int mctp_rtm_getneigh(struct sk_buff *skb, struct netlink_callback *cb)
                int idx;
        } *cbctx = (void *)cb->ctx;
 
-       ndmsg = nlmsg_data(cb->nlh);
+       ndmsg = nlmsg_payload(cb->nlh, sizeof(*ndmsg));
+       if (!ndmsg)
+               return -EINVAL;
+
        req_ifindex = ndmsg->ndm_ifindex;
 
        idx = 0;