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Date: Wed, 14 Sep 2016 12:32:53 +0200
From: u-uy74@...ey.se
To: musl@...ts.openwall.com
Subject: Re: incompatibility between libtheora/mmx and musl ?
On Tue, Sep 13, 2016 at 04:43:04PM -0400, Rich Felker wrote:
> > Libtheora contains an assembler part for ia32 and x86_64 which has been
> > in use for many years, with at least both glibc and uclibc.
> >
> > Now, musl-based builds of libtheora for ia32 with this code enabled
> > lead to the encoder segfaulting. No problem when using the C version.
> > https://trac.xiph.org/ticket/2287
> >
> > There is also a corresponding
> >
> > https://bugs.alpinelinux.org/issues/6132
>
> The most likely explanation is that they're overflowing a heap buffer.
> Perhaps it would be possible to pad all their malloc/realloc calls
> with +64 or so to see if that makes the problem go away. If so that
> gives a good starting point for tracking down the bug.
Thanks for the suggestion, indeed libtheora seems to consistently use
ogg_malloc() which is redefinable.
Building with
#define _ogg_malloc(x) malloc((x)+256)
#define _ogg_calloc(x,y) calloc((x)+256,(y))
#define _ogg_realloc(y,x) realloc((y),(x)+256)
#define _ogg_free free
instead of the default
#define _ogg_malloc malloc
#define _ogg_calloc calloc
#define _ogg_realloc realloc
#define _ogg_free free
did not make any difference. The crash on a test file occurs in the same
way and the resulting partial output file is as long as otherwise.
This may mean that this is not a simple overflowing but rather
overwriting or reading distant "random" places (?) (register corruption?)
Rune
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