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authorMike DePaulo <mikedep333@gmail.com>2015-02-08 20:01:27 -0500
committerMike DePaulo <mikedep333@gmail.com>2015-05-30 21:58:57 -0400
commitc2298e0757106c03f2a9a95d5493102f33c3cfdb (patch)
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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)
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