Thu Oct 10 01:58:46 PDT 2013

1 files changed, 76 insertions, 0 deletions

diff --git a/extra/xorg-server/0001-Avoid-use-after-free-in-dix-dixfonts.c-doImageText-C.patch b/extra/xorg-server/0001-Avoid-use-after-free-in-dix-dixfonts.c-doImageText-C.patch
new file mode 100644
index 000000000..b550bcedd
--- /dev/null
+++ b/extra/xorg-server/0001-Avoid-use-after-free-in-dix-dixfonts.c-doImageText-C.patch
@@ -0,0 +1,76 @@
+From 7bddc2ba16a2a15773c2ea8947059afa27727764 Mon Sep 17 00:00:00 2001
+From: Alan Coopersmith <alan.coopersmith@oracle.com>
+Date: Mon, 16 Sep 2013 21:47:16 -0700
+Subject: [PATCH] Avoid use-after-free in dix/dixfonts.c: doImageText()
+ [CVE-2013-4396]
+
+Save a pointer to the passed in closure structure before copying it
+and overwriting the *c pointer to point to our copy instead of the
+original.  If we hit an error, once we free(c), reset c to point to
+the original structure before jumping to the cleanup code that
+references *c.
+
+Since one of the errors being checked for is whether the server was
+able to malloc(c->nChars * itemSize), the client can potentially pass
+a number of characters chosen to cause the malloc to fail and the
+error path to be taken, resulting in the read from freed memory.
+
+Since the memory is accessed almost immediately afterwards, and the
+X server is mostly single threaded, the odds of the free memory having
+invalid contents are low with most malloc implementations when not using
+memory debugging features, but some allocators will definitely overwrite
+the memory there, leading to a likely crash.
+
+Reported-by: Pedro Ribeiro <pedrib@gmail.com>
+Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
+Reviewed-by: Julien Cristau <jcristau@debian.org>
+---
+ dix/dixfonts.c |    5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/dix/dixfonts.c b/dix/dixfonts.c
+index feb765d..2e34d37 100644
+--- a/dix/dixfonts.c
++++ b/dix/dixfonts.c
+@@ -1425,6 +1425,7 @@ doImageText(ClientPtr client, ITclosurePtr c)
+             GC *pGC;
+             unsigned char *data;
+             ITclosurePtr new_closure;
++            ITclosurePtr old_closure;
+ 
+             /* We're putting the client to sleep.  We need to
+                save some state.  Similar problem to that handled
+@@ -1436,12 +1437,14 @@ doImageText(ClientPtr client, ITclosurePtr c)
+                 err = BadAlloc;
+                 goto bail;
+             }
++            old_closure = c;
+             *new_closure = *c;
+             c = new_closure;
+ 
+             data = malloc(c->nChars * itemSize);
+             if (!data) {
+                 free(c);
++                c = old_closure;
+                 err = BadAlloc;
+                 goto bail;
+             }
+@@ -1452,6 +1455,7 @@ doImageText(ClientPtr client, ITclosurePtr c)
+             if (!pGC) {
+                 free(c->data);
+                 free(c);
++                c = old_closure;
+                 err = BadAlloc;
+                 goto bail;
+             }
+@@ -1464,6 +1468,7 @@ doImageText(ClientPtr client, ITclosurePtr c)
+                 FreeScratchGC(pGC);
+                 free(c->data);
+                 free(c);
++                c = old_closure;
+                 err = BadAlloc;
+                 goto bail;
+             }
+-- 
+1.7.9.2
+