netfilter: nfnetlink_log: fix uninitialized padding leak in NFULA_PAYLOAD

__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: df6fb86 ("[NETFILTER]: nfnetlink: convert to generic netlink attribute functions")
Reported-by: Xiang Mei <[email protected]>
Signed-off-by: Weiming Shi <[email protected]>
Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: winmin

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();
 	}