Subject: [PATCH 19/25] net: sched: fix NULL pointer dereference when action calls some targets

From: Xin Long <[email-masked]>
Date: Fri, 18 Aug 2017 11:01:36 +0800

[ Upstream commit 4f8a881acc9d1adaf1e552349a0b1df28933a04c ]

As we know in some target's checkentry it may dereference par.entryinfo
to check entry stuff inside. But when sched action calls xt_check_target,
par.entryinfo is set with NULL. It would cause kernel panic when calling
some targets.

It can be reproduce with:
  # tc qd add dev eth1 ingress handle ffff:
  # tc filter add dev eth1 parent ffff: u32 match u32 0 0 action xt \
    -j ECN --ecn-tcp-remove

It could also crash kernel when using target CLUSTERIP or TPROXY.

By now there's no proper value for par.entryinfo in ipt_init_target,
but it can not be set with NULL. This patch is to void all these
panics by setting it with an ipt_entry obj with all members = 0.

Note that this issue has been there since the very beginning.

Signed-off-by: Xin Long <[email-masked]>
Acked-by: Pablo Neira Ayuso <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/sched/act_ipt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
index a1aec0a6c789..50030519a89b 100644
--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c
@@ -41,6 +41,7 @@ static int ipt_init_target(struct xt_entry_target *t, char *table,
 {
 	struct xt_tgchk_param par;
 	struct xt_target *target;
+	struct ipt_entry e = {};
 	int ret = 0;
 
 	target = xt_request_find_target(AF_INET, t->u.user.name,
@@ -51,6 +52,7 @@ static int ipt_init_target(struct xt_entry_target *t, char *table,
 	t->u.kernel.target = target;
 	memset(&par, 0, sizeof(par));
 	par.table     = table;
+	par.entryinfo = &e;
 	par.target    = target;
 	par.targinfo  = t->data;
 	par.hook_mask = hook;
-- 
2.13.5