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

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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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> >
> > --- 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@xxxxxxxxx>

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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