Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang [off-list ref] wrote:

(Cc'ing netfilter and Jamal)

On Sat, Aug 5, 2017 at 4:35 AM, Xin Long [off-list ref] wrote:

quoted

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.

[1]

quoted

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.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sched/act_ipt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
index 7c4816b..0f09f70 100644
--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c

@@ -41,6 +41,7 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
 {
        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,

@@ -48,10 +49,11 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
        if (IS_ERR(target))
                return PTR_ERR(target);

+       memset(&e, 0, sizeof(e));
        t->u.kernel.target = target;
        par.net       = net;
        par.table     = table;
-       par.entryinfo = NULL;
+       par.entryinfo = &e;

This looks like a completely API burden?

netfilter xt targets are not really compatible with netsched action.
I've got to say, the patch is just a way to make checkentry return
false and avoid panic. like [1] said