[PATCH nf] netfilter: x_tables: initialise match/target check parameter struct

[Florian Westphal]

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+da4494182233c23a5...@syzkaller.appspotmail.com
Fixes: 55917a21d0cc0 ("netfilter: x_tables: add context to know if extension 
runs from nft_compat")
Signed-off-by: Florian Westphal <f...@strlen.de>
---
 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(+)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index c2138e7e8263..93600aa606a8 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -709,6 +709,8 @@ ebt_check_entry(struct ebt_entry *e, struct net *net,
        }
        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;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 38ab97b0a2ec..ca0dad90803a 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -531,6 +531,7 @@ find_check_entry(struct ipt_entry *e, struct net *net, 
const char *name,
                return -ENOMEM;
 
        j = 0;
+       memset(&mtpar, 0, sizeof(mtpar));
        mtpar.net       = net;
        mtpar.table     = name;
        mtpar.entryinfo = &e->ip;
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 0758b5bcfb29..7eab959734bc 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -550,6 +550,7 @@ find_check_entry(struct ip6t_entry *e, struct net *net, 
const char *name,
                return -ENOMEM;
 
        j = 0;
+       memset(&mtpar, 0, sizeof(mtpar));
        mtpar.net       = net;
        mtpar.table     = name;
        mtpar.entryinfo = &e->ipv6;
-- 
2.16.4

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