[X2Go-Commits] [nx-libs] 24/40: Avoid use-after-free in dix/dixfonts.c: doImageText() [CVE-2013-4396] from xorg/Xserver http://lists.x.org/archives/xorg-announce/2013-October/002332.html

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Sat Jun 20 00:03:27 CEST 2015


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x2go pushed a commit to branch 3.6.x
in repository nx-libs.

commit c2298e0757106c03f2a9a95d5493102f33c3cfdb
Author: Mike DePaulo <mikedep333 at gmail.com>
Date:   Sun Feb 8 20:01:27 2015 -0500

    Avoid use-after-free in dix/dixfonts.c: doImageText() [CVE-2013-4396] from xorg/Xserver http://lists.x.org/archives/xorg-announce/2013-October/002332.html
    
    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.
    
    v2: Apply to NXdixfonts.c rather than dixfonts.c (Mike DePaulo)
---
 nx-X11/programs/Xserver/hw/nxagent/NXdixfonts.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/nx-X11/programs/Xserver/hw/nxagent/NXdixfonts.c b/nx-X11/programs/Xserver/hw/nxagent/NXdixfonts.c
index 9224436..5622f8c 100644
--- a/nx-X11/programs/Xserver/hw/nxagent/NXdixfonts.c
+++ b/nx-X11/programs/Xserver/hw/nxagent/NXdixfonts.c
@@ -1694,6 +1694,7 @@ doImageText(ClientPtr client, register 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
@@ -1706,6 +1707,7 @@ doImageText(ClientPtr client, register ITclosurePtr c)
 		err = BadAlloc;
 		goto bail;
 	    }
+	    old_closure = c;
 	    *new_closure = *c;
 	    c = new_closure;
 
@@ -1713,6 +1715,7 @@ doImageText(ClientPtr client, register ITclosurePtr c)
 	    if (!data)
 	    {
 		xfree(c);
+		c = old_closure;
 		err = BadAlloc;
 		goto bail;
 	    }
@@ -1724,6 +1727,7 @@ doImageText(ClientPtr client, register ITclosurePtr c)
 	    {
 		xfree(c->data);
 		xfree(c);
+		c = old_closure;
 		err = BadAlloc;
 		goto bail;
 	    }
@@ -1742,6 +1746,7 @@ doImageText(ClientPtr client, register ITclosurePtr c)
 		FreeScratchGC(pGC);
 		xfree(c->data);
 		xfree(c);
+		c = old_closure;
 		err = BadAlloc;
 		goto bail;
 	    }

--
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