[PATCH 4.12 24/99] net: sched: fix NULL pointer dereference when action calls some targets

Greg Kroah-Hartman
2017-08-28T09:21:29Z

From: Xin Long <lucien.xin@gmail.com>

[ 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 <lucien.xin@gmail.com>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/act_ipt.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c
@@ -41,6 +41,7 @@ static int ipt_init_target(struct net *n
{
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,
@@ -52,6 +53,7 @@ static int ipt_init_target(struct net *n
memset(&par, 0, sizeof(par));
par.net = net;
par.table = table;
+ par.entryinfo = &e;
par.target = target;
par.targinfo = t->data;
par.hook_mask = hook;