netdev - Re: [PATCH 1/1] net: fix cipso packet validation when !NETLABEL

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Date:	Fri, 11 Oct 2013 15:02:10 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	Seif Mazareeb <seif@...vell.com>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>,
	Dmitri Epshtein <dima@...vell.com>
Subject: Re: [PATCH 1/1] net: fix cipso packet validation when !NETLABEL

On Friday, October 11, 2013 10:58:31 AM Seif Mazareeb wrote:
> When CONFIG_NETLABEL is disabled, the cipso_v4_validate() function could
> loop forever in the main loop if opt[opt_iter +1] == 0, this will causing a
> kernel crash in an SMP system, since the CPU executing this function will
> stall /not respond to IPIs.
> 
> This problem can be reproduced by running the IP Stack Integrity Checker
> (http://isic.sourceforge.net) using the following command on a Linux machine
> connected to DUT:
> 
> "icmpsic -s rand -d <DUT IP address> -r 123456"
> wait (1-2 min)
> 
> Signed-off-by: Seif Mazareeb <seif@...vell.com>
> ---
>  include/net/cipso_ipv4.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/net/cipso_ipv4.h b/include/net/cipso_ipv4.h
> index a7a683e..047f1f6 100644
> --- a/include/net/cipso_ipv4.h
> +++ b/include/net/cipso_ipv4.h
> @@ -306,6 +306,10 @@ static inline int cipso_v4_validate(const struct
> sk_buff *skb, err_offset = opt_iter + 1;
>                         goto out;
>                 }
> +
> +               if (opt[opt_iter + 1] == 0)
> +                       break;
> +
>                 opt_iter += opt[opt_iter + 1];
>         }

Thanks for finding and reporting this bug.  Unfortunately, I don't think the 
supplied patch is the best way to solve this.  Since a length of zero is not 
valid for any known CIPSO tag types (at least that I am aware of), we should 
treat a zero length tag as an error, similar to how we treat tags with length 
values that stretch beyond the option itself.

I'm thinking something like this:

static inline int cipso_v4_validate(const struct sk_buff *skb,
                                    unsigned char **option)
{
        unsigned char *opt = *option;
        unsigned char err_offset = 0;
        u8 opt_len = opt[1];
        u8 opt_iter;
        u8 tag_len;

        if (opt_len < 8) {
                err_offset = 1;
                goto out;
        }

        if (get_unaligned_be32(&opt[2]) == 0) {
                err_offset = 2;
                goto out;
        }

        for (opt_iter = 6; opt_iter < opt_len;) {
                tag_len = opt[opt_iter + 1];
                if ((tag_len == 0) || (tag_len > (opt_len - opt_iter))) {
                        err_offset = opt_iter + 1;
                        goto out;
                }
                opt_iter += tag_len;
        }

out:
        *option = opt + err_offset;
        return err_offset;

}

If you want to fixup your patch that would be appreciated, if not, please let 
me know so I can submit the fix.

Thanks,
-Paul

-- 
paul moore
www.paul-moore.com

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