[PATCH net 03/12] netfilter: nfnetlink_log: fix uninitialized padding leak in NFULA_PAYLOAD

Pablo Neira Ayuso
2026-03-26T12:52:03Z

From: Weiming Shi <bestswngs@gmail.com>

__build_packet_message() manually constructs the NFULA_PAYLOAD netlink
attribute using skb_put() and skb_copy_bits(), bypassing the standard
nla_reserve()/nla_put() helpers. While nla_total_size(data_len) bytes
are allocated (including NLA alignment padding), only data_len bytes
of actual packet data are copied. The trailing nla_padlen(data_len)
bytes (1-3 when data_len is not 4-byte aligned) are never initialized,
leaking stale heap contents to userspace via the NFLOG netlink socket.

Replace the manual attribute construction with nla_reserve(), which
handles the tailroom check, header setup, and padding zeroing via
__nla_reserve(). The subsequent skb_copy_bits() fills in the payload
data on top of the properly initialized attribute.

Fixes: df6fb868d611 ("[NETFILTER]: nfnetlink: convert to generic netlink attribute functions")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
net/netfilter/nfnetlink_log.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index b35a90955e2e..fcbe54940b2e 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -647,15 +647,11 @@ __build_packet_message(struct nfnl_log_net *log,

if (data_len) {
struct nlattr *nla;
- int size = nla_attr_size(data_len);

- if (skb_tailroom(inst->skb) < nla_total_size(data_len))
+ nla = nla_reserve(inst->skb, NFULA_PAYLOAD, data_len);
+ if (!nla)
goto nla_put_failure;

- nla = skb_put(inst->skb, nla_total_size(data_len));
- nla->nla_type = NFULA_PAYLOAD;
- nla->nla_len = size;
-
if (skb_copy_bits(skb, 0, nla_data(nla), data_len))
BUG();
}
--
2.47.3