[PATCH net] net/sched: act_pedit: limit negative offset

[Amir Vadai]

Should not allow setting a negative offset that goes below the skb head.

Signed-off-by: Amir Vadai <a...@vadai.me>
---
Hi Dave,

Please pull to -stable branches.

Thanks,
Amir

 net/sched/act_pedit.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
index b54d56d4959b..e79e8a88f2d2 100644
--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -154,8 +154,11 @@ static int tcf_pedit(struct sk_buff *skb, const struct 
tc_action *a,
                        }
 
                        ptr = skb_header_pointer(skb, off + offset, 4, &_data);
-                       if (!ptr)
+                       if ((unsigned char *)ptr < skb->head) {
+                               pr_info("tc filter pedit offset out of 
bounds\n");
                                goto bad;
+                       }
+
                        /* just do it, baby */
                        *ptr = ((*ptr & tkey->mask) ^ tkey->val);
                        if (ptr == &_data)
-- 
2.10.2