net: nexthop: Initialize all fields in dumped nexthops

jira LE-2157
cve CVE-2024-42283
Rebuild_History Non-Buildable kernel-5.14.0-503.14.1.el9_5
commit-author Petr Machata <[email protected]>
commit 6d745cd

struct nexthop_grp contains two reserved fields that are not initialized by
nla_put_nh_group(), and carry garbage. This can be observed e.g. with
strace (edited for clarity):

    # ip nexthop add id 1 dev lo
    # ip nexthop add id 101 group 1
    # strace -e recvmsg ip nexthop get id 101
    ...
    recvmsg(... [{nla_len=12, nla_type=NHA_GROUP},
                 [{id=1, weight=0, resvd1=0x69, resvd2=0x67}]] ...) = 52

The fields are reserved and therefore not currently used. But as they are, they
leak kernel memory, and the fact they are not just zero complicates repurposing
of the fields for new ends. Initialize the full structure.

Fixes: 430a049 ("nexthop: Add support for nexthop groups")
	Signed-off-by: Petr Machata <[email protected]>
	Reviewed-by: Ido Schimmel <[email protected]>
	Reviewed-by: Eric Dumazet <[email protected]>
	Signed-off-by: David S. Miller <[email protected]>
(cherry picked from commit 6d745cd)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

net/ipv4/nexthop.c

@@ -676,9 +676,10 @@ static int nla_put_nh_group(struct sk_buff *skb, struct nh_group *nhg)
 
 	p = nla_data(nla);
 	for (i = 0; i < nhg->num_nh; ++i) {
-		p->id = nhg->nh_entries[i].nh->id;
-		p->weight = nhg->nh_entries[i].weight - 1;
-		p += 1;
+		*p++ = (struct nexthop_grp) {
+			.id = nhg->nh_entries[i].nh->id,
+			.weight = nhg->nh_entries[i].weight - 1,
+		};
 	}
 
 	if (nhg->resilient && nla_put_nh_group_res(skb, nhg))