[PATCH 4.9 28/32] netfilter: x_tables: initialise match/target check parameter struct

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@strlen.de>

commit c568503ef02030f169c9e19204def610a3510918 upstream.

syzbot reports following splat:

BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
 net/bridge/netfilter/ebt_stp.c:162
 ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
 xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
 ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
 ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]

The uninitialised access is
   xt_mtchk_param->nft_compat

... which should be set to 0.
Fix it by zeroing the struct beforehand, same for tgchk.

ip(6)tables targetinfo uses c99-style initialiser, so no change
needed there.

Reported-by: syzbot+da4494182233c23a5fcf@syzkaller.appspotmail.com
Fixes: 55917a21d0cc0 ("netfilter: x_tables: add context to know if extension runs from nft_compat")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/bridge/netfilter/ebtables.c |    2 ++
 net/ipv4/netfilter/ip_tables.c  |    1 +
 net/ipv6/netfilter/ip6_tables.c |    1 +
 3 files changed, 4 insertions(+)

--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -704,6 +704,8 @@ ebt_check_entry(struct ebt_entry *e, str
 	}
 	i = 0;
 
+	memset(&mtpar, 0, sizeof(mtpar));
+	memset(&tgpar, 0, sizeof(tgpar));
 	mtpar.net	= tgpar.net       = net;
 	mtpar.table     = tgpar.table     = name;
 	mtpar.entryinfo = tgpar.entryinfo = e;
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -554,6 +554,7 @@ find_check_entry(struct ipt_entry *e, st
 		return -ENOMEM;
 
 	j = 0;
+	memset(&mtpar, 0, sizeof(mtpar));
 	mtpar.net	= net;
 	mtpar.table     = name;
 	mtpar.entryinfo = &e->ip;
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -584,6 +584,7 @@ find_check_entry(struct ip6t_entry *e, s
 		return -ENOMEM;
 
 	j = 0;
+	memset(&mtpar, 0, sizeof(mtpar));
 	mtpar.net	= net;
 	mtpar.table     = name;
 	mtpar.entryinfo = &e->ipv6;