netdev - [PATCH net] net: nexthop: Initialize all fields in dumped nexthops

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Message-ID: <8b06dd4ec057d912ca3947bacf15529272dea796.1721749627.git.petrm@nvidia.com>
Date: Tue, 23 Jul 2024 18:04:16 +0200
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, <netdev@...r.kernel.org>
CC: David Ahern <dsahern@...nel.org>, Petr Machata <petrm@...dia.com>,
	<mlxsw@...dia.com>, Ido Schimmel <idosch@...dia.com>
Subject: [PATCH net] net: nexthop: Initialize all fields in dumped nexthops

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: 430a049190de ("nexthop: Add support for nexthop groups")
Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/ipv4/nexthop.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
index 535856b0f0ed..6b9787ee8601 100644
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -888,9 +888,10 @@ static int nla_put_nh_group(struct sk_buff *skb, struct nexthop *nh,
 
 	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))
-- 
2.45.0