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