netfilter: xt_nfacct: Fix alignment mismatch in xt_nfacct_match_info

When running a 64-bit kernel with a 32-bit iptables binary, the size of
the xt_nfacct_match_info struct diverges.

kernel: sizeof(struct xt_nfacct_match_info) : 40
iptables: sizeof(struct xt_nfacct_match_info)) : 36

Trying to append nfacct related rules results in an unhelpful message.
Although it is suggested to look for more information in dmesg, nothing
can be found there.

# iptables -A <chain> -m nfacct --nfacct-name <acct-object>
iptables: Invalid argument. Run `dmesg' for more information.

This patch fixes the memory misalignment by enforcing 8-byte alignment
within the struct's first revision. This solution is often used in many
other uapi netfilter headers.

Signed-off-by: Juliana Rodrigueiro <[e-mail]>
Acked-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/xt_nfacct.h

···
 	struct nf_acct	*nfacct;
 };
 
+struct xt_nfacct_match_info_v1 {
+	char		name[NFACCT_NAME_MAX];
+	struct nf_acct	*nfacct __attribute__((aligned(8)));
+};
+
 #endif /* _XT_NFACCT_MATCH_H */

net/netfilter/xt_nfacct.c

···
 	nfnl_acct_put(info->nfacct);
 }
 
-static struct xt_match nfacct_mt_reg __read_mostly = {
-	.name       = "nfacct",
-	.family     = NFPROTO_UNSPEC,
-	.checkentry = nfacct_mt_checkentry,
-	.match      = nfacct_mt,
-	.destroy    = nfacct_mt_destroy,
-	.matchsize  = sizeof(struct xt_nfacct_match_info),
-	.usersize   = offsetof(struct xt_nfacct_match_info, nfacct),
-	.me         = THIS_MODULE,
+static struct xt_match nfacct_mt_reg[] __read_mostly = {
+	{
+		.name       = "nfacct",
+		.revision   = 0,
+		.family     = NFPROTO_UNSPEC,
+		.checkentry = nfacct_mt_checkentry,
+		.match      = nfacct_mt,
+		.destroy    = nfacct_mt_destroy,
+		.matchsize  = sizeof(struct xt_nfacct_match_info),
+		.usersize   = offsetof(struct xt_nfacct_match_info, nfacct),
+		.me         = THIS_MODULE,
+	},
+	{
+		.name       = "nfacct",
+		.revision   = 1,
+		.family     = NFPROTO_UNSPEC,
+		.checkentry = nfacct_mt_checkentry,
+		.match      = nfacct_mt,
+		.destroy    = nfacct_mt_destroy,
+		.matchsize  = sizeof(struct xt_nfacct_match_info_v1),
+		.usersize   = offsetof(struct xt_nfacct_match_info_v1, nfacct),
+		.me         = THIS_MODULE,
+	},
 };
 
 static int __init nfacct_mt_init(void)
 {
-	return xt_register_match(&nfacct_mt_reg);
+	return xt_register_matches(nfacct_mt_reg, ARRAY_SIZE(nfacct_mt_reg));
 }
 
 static void __exit nfacct_mt_exit(void)
 {
-	xt_unregister_match(&nfacct_mt_reg);
+	xt_unregister_matches(nfacct_mt_reg, ARRAY_SIZE(nfacct_mt_reg));
 }
 
 module_init(nfacct_mt_init);