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Date: Thu, 04 Nov 2010 09:54:53 +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
On Wed, 2010-11-03 at 12:12 +1100, Andrew Hendry wrote:
> 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);
> >
> >
> >
How does this look? It appears to fix it for the cases I could test.
Signed-of-by: Andrew Hendry <andrew.hendry@...il.com>
diff --git a/net/x25/x25_facilities.c b/net/x25/x25_facilities.c
index 771bab0..3a8c4c4 100644
--- a/net/x25/x25_facilities.c
+++ b/net/x25/x25_facilities.c
@@ -134,15 +134,15 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
case X25_FAC_CLASS_D:
switch (*p) {
case X25_FAC_CALLING_AE:
- if (p[1] > X25_MAX_DTE_FACIL_LEN)
- break;
+ if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1)
+ return 0;
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)
- break;
+ if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1)
+ return 0;
dte_facs->called_len = p[2];
memcpy(dte_facs->called_ae, &p[3], p[1] - 1);
*vc_fac_mask |= X25_MASK_CALLED_AE;
diff --git a/net/x25/x25_in.c b/net/x25/x25_in.c
index 6317896..1d80e10 100644
--- a/net/x25/x25_in.c
+++ b/net/x25/x25_in.c
@@ -119,6 +119,8 @@ static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametyp
&x25->vc_facil_mask);
if (len > 0)
skb_pull(skb, len);
+ else
+ return -1;
/*
* Copy any Call User Data.
*/
--
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