linux-kernel - Re: [PATCH] Cipso: cipso_v4

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Date:   Fri, 28 Jul 2017 11:12:43 -0400
From:   Paul Moore <pmoore@...hat.com>
To:     Yujuan Qi <yujuan.qi@...iatek.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Casey Schaufler <casey@...aufler-ca.com>,
        netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Ryder Lee <ryder.lee@...iatek.com>
Subject: Re: [PATCH] Cipso: cipso_v4_optptr enter infinite loop

On Fri, Jul 28, 2017 at 7:30 AM, Yujuan Qi <yujuan.qi@...iatek.com> wrote:
> From: "yujuan.qi" <yujuan.qi@...iatek.com>
>
> in for(),if((optlen > 0) && (optptr[1] == 0)), enter infinite loop.
>
> Test: receive a packet which the ip length > 20 and the first byte of ip option is 0, produce this issue
>
> Signed-off-by: yujuan.qi <yujuan.qi@...iatek.com>
> ---
>  net/ipv4/cipso_ipv4.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
> index ae20616..b3d97c7 100644
> --- a/net/ipv4/cipso_ipv4.c
> +++ b/net/ipv4/cipso_ipv4.c
> @@ -1528,6 +1528,8 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
>                 taglen = optptr[1];
>                 optlen -= taglen;
>                 optptr += taglen;
> +               if (!taglen)
> +                       break;
>         }
>
>         return NULL;

Thanks for catching this and submitting a patch.  Unfortunately
checking taglen/optptr[1] isn't going to help with the NOP and EOL
options as they are single byte options.  I think a for-loop like the
following, or something similar, is probably the better solution:

  for (optlen = iph->ihl*4 - sizeof(struct iphdr); optlen > 0; ) {
         switch (optptr[0]) {
         case IPOPT_CIPSO:
                 return optptr;
         case IPOPT_END:
                 return NULL;
         case IPOPT_NOOP:
                 taglen = 1;
                 break;
         default:
                 taglen = optptr[1];
         }
         optlen -= taglen;
         optptr += taglen;
  }

-- 
paul moore
security @ redhat