[PATCH 4.8 16/45] net/sched: pedit: make sure that offset is valid

[Greg Kroah-Hartman]

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Amir Vadai <a...@vadai.me>


[ Upstream commit 95c2027bfeda21a28eb245121e6a249f38d0788e ]

Add a validation function to make sure offset is valid:
1. Not below skb head (could happen when offset is negative).
2. Validate both 'offset' and 'at'.

Signed-off-by: Amir Vadai <a...@vadai.me>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/sched/act_pedit.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -108,6 +108,17 @@ static void tcf_pedit_cleanup(struct tc_
        kfree(keys);
 }
 
+static bool offset_valid(struct sk_buff *skb, int offset)
+{
+       if (offset > 0 && offset > skb->len)
+               return false;
+
+       if  (offset < 0 && -offset > skb_headroom(skb))
+               return false;
+
+       return true;
+}
+
 static int tcf_pedit(struct sk_buff *skb, const struct tc_action *a,
                     struct tcf_result *res)
 {
@@ -134,6 +145,11 @@ static int tcf_pedit(struct sk_buff *skb
                        if (tkey->offmask) {
                                char *d, _d;
 
+                               if (!offset_valid(skb, off + tkey->at)) {
+                                       pr_info("tc filter pedit 'at' offset %d 
out of bounds\n",
+                                               off + tkey->at);
+                                       goto bad;
+                               }
                                d = skb_header_pointer(skb, off + tkey->at, 1,
                                                       &_d);
                                if (!d)
@@ -146,10 +162,10 @@ static int tcf_pedit(struct sk_buff *skb
                                        " offset must be on 32 bit 
boundaries\n");
                                goto bad;
                        }
-                       if (offset > 0 && offset > skb->len) {
-                               pr_info("tc filter pedit"
-                                       " offset %d can't exceed pkt length 
%d\n",
-                                      offset, skb->len);
+
+                       if (!offset_valid(skb, off + offset)) {
+                               pr_info("tc filter pedit offset %d out of 
bounds\n",
+                                       offset);
                                goto bad;
                        }