netdev - Re: [SECURITY] memory corruption in X.25 facilities parsing

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Message-ID: <AANLkTi=fAMDP-rGZfOcHS0j_J=KSBgxqqbLaQsXxooJn@mail.gmail.com>
Date:	Wed, 3 Nov 2010 12:12:51 +1100
From:	Andrew Hendry <andrew.hendry@...il.com>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	netdev@...r.kernel.org, security@...nel.org, stable@...nel.org
Subject: Re: [SECURITY] memory corruption in X.25 facilities parsing

There is an issue here, under select scenarios I can crash systems.
However the patch doesn't resolve it fully, I think after breaking at
that point the len and p pointers are messed up before it tries to
parse the next facility.

Maybe it should return not break? It should reject/clear such calls.
I'll start checking if the callers properly handle errors.
Also should it be if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1),
because it does the memcpy with p[1] -1


On Wed, Nov 3, 2010 at 2:02 AM, Dan Rosenberg <drosenberg@...curity.com> wrote:
> I put this together after a quick glance, so if someone knows this code
> better than I do (i.e. at all), feel free to comment or drop this patch
> if it's unnecessary.
>
> A value of 0 will cause a memcpy() of ULONG_MAX size, destroying the
> kernel heap.
>
> Signed-off-by: Dan Rosenberg <drosenberg@...curity.com>
>
> --- linux-2.6.36-rc6.orig/net/x25/x25_facilities.c      2010-09-28 21:01:22.000000000 -0400
> +++ linux-2.6.36-rc6/net/x25/x25_facilities.c   2010-11-02 10:36:02.827291324 -0400
> @@ -134,14 +134,14 @@ int x25_parse_facilities(struct sk_buff
>                case X25_FAC_CLASS_D:
>                        switch (*p) {
>                        case X25_FAC_CALLING_AE:
> -                               if (p[1] > X25_MAX_DTE_FACIL_LEN)
> +                               if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] == 0)
>                                        break;
>                                dte_facs->calling_len = p[2];
>                                memcpy(dte_facs->calling_ae, &p[3], p[1] - 1);
>                                *vc_fac_mask |= X25_MASK_CALLING_AE;
>                                break;
>                        case X25_FAC_CALLED_AE:
> -                               if (p[1] > X25_MAX_DTE_FACIL_LEN)
> +                               if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] == 0)
>                                        break;
>                                dte_facs->called_len = p[2];
>                                memcpy(dte_facs->called_ae, &p[3], p[1] - 1);
>
>
>
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