netdev - Re: [PATCH net V2] net/sched: pedit: make sure that offset is valid

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Date:   Tue, 29 Nov 2016 17:27:05 +0800
From:   zhuyj <zyjzyj2000@...il.com>
To:     Amir Vadai <amir@...ai.me>
Cc:     "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Hadar Har-Zion <hadarh@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net V2] net/sched: pedit: make sure that offset is valid

 Thanks a lot.
When will offset become -1?

On Tue, Nov 29, 2016 at 3:14 PM, Amir Vadai <amir@...ai.me> wrote:
> On Tue, Nov 29, 2016 at 10:32:05AM +0800, zhuyj wrote:
>>  +       if (offset > 0 && offset > skb->len)
>>
>> offset > skb->len is enough?
> offset is signed and skb->len is unsigned. Therefore for example if
> offset=-1 and skb->len=10, the actual comparison is 0xff...>10
>
>>
>> On Mon, Nov 28, 2016 at 6:56 PM, Amir Vadai <amir@...ai.me> wrote:
>> > 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 <amir@...ai.me>
>> > ---
>> > Hi Dave,
>> >
>> > Please pull to -stable branches.
>> >
>> > Changes from V0:
>> > - Add a validation to the 'at' value (this is used as an offset too)
>> > - Instead of validating the output of skb_header_pointer(), make sure that the
>> >         offset is good before calling it.
>> >
>> > Thanks,
>> > Amir
>> >  net/sched/act_pedit.c | 24 ++++++++++++++++++++----
>> >  1 file changed, 20 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
>> > index b54d56d4959b..cf9b2fe8eac6 100644
>> > --- a/net/sched/act_pedit.c
>> > +++ b/net/sched/act_pedit.c
>> > @@ -108,6 +108,17 @@ static void tcf_pedit_cleanup(struct tc_action *a, int bind)
>> >         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, const struct tc_action *a,
>> >                         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, const struct tc_action *a,
>> >                                         " 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;
>> >                         }
>> >
>> > --
>> > 2.10.2
>> >