Subject: [PATCH AUTOSEL 6.18] netfilter: nfnetlink_log: initialize nfgenmsg in NLMSG_DONE terminator

From: Sasha Levin <[email-masked]>
Date: Mon, 20 Apr 2026 09:17:45 -0400

From: Xiang Mei <[email-masked]>

[ Upstream commit 1f3083aec8836213da441270cdb1ab612dd82cf4 ]

When batching multiple NFLOG messages (inst->qlen > 1), __nfulnl_send()
appends an NLMSG_DONE terminator with sizeof(struct nfgenmsg) payload via
nlmsg_put(), but never initializes the nfgenmsg bytes. The nlmsg_put()
helper only zeroes alignment padding after the payload, not the payload
itself, so four bytes of stale kernel heap data are leaked to userspace
in the NLMSG_DONE message body.

Use nfnl_msg_put() to build the NLMSG_DONE terminator, which initializes
the nfgenmsg payload via nfnl_fill_hdr(), consistent with how
__build_packet_message() already constructs NFULNL_MSG_PACKET headers.

Fixes: 29c5d4afba51 ("[NETFILTER]: nfnetlink_log: fix sending of multipart messages")
Reported-by: Weiming Shi <[email-masked]>
Signed-off-by: Xiang Mei <[email-masked]>
Signed-off-by: Florian Westphal <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 net/netfilter/nfnetlink_log.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index dcd2493a9a404..b1f3eda85989c 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -361,10 +361,10 @@ static void
 __nfulnl_send(struct nfulnl_instance *inst)
 {
 	if (inst->qlen > 1) {
-		struct nlmsghdr *nlh = nlmsg_put(inst->skb, 0, 0,
-						 NLMSG_DONE,
-						 sizeof(struct nfgenmsg),
-						 0);
+		struct nlmsghdr *nlh = nfnl_msg_put(inst->skb, 0, 0,
+						    NLMSG_DONE, 0,
+						    AF_UNSPEC, NFNETLINK_V0,
+						    htons(inst->group_num));
 		if (WARN_ONCE(!nlh, "bad nlskb size: %u, tailroom %d\n",
 			      inst->skb->len, skb_tailroom(inst->skb))) {
 			kfree_skb(inst->skb);
-- 
2.53.0