From: u-uy74@aetey.se
To: musl@lists.openwall.com
Subject: Re: incompatibility between libtheora/mmx and musl ?
Date: Wed, 14 Sep 2016 16:04:50 +0200 [thread overview]
Message-ID: <20160914140450.GQ16436@example.net> (raw)
In-Reply-To: <20160914112400.GS1280@port70.net>
On Wed, Sep 14, 2016 at 01:24:00PM +0200, Szabolcs Nagy wrote:
> > #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?)
> can be underflow (or the way they align the pointer returned by malloc)
Pointer alignment yes they do in some cases but in a different layer,
inside the malloc()-ed buffers, it is plain C and looks harmless to me.
> you can increase/decrease alignment of musl's alloc by
> changing SIZE_ALIGN in src/malloc/malloc.c
Doubling the alignment did not apparently change the crashing.
Reducing the alignment in half did not apparently change the crashing.
(A single test file with a single quality setting tested
crashed the same way, at the same place in the output stream)
> (or you can try some hack in _ogg_malloc/free if you are
> sure that's what they are using)
Yes it is present/used for this very purpose, to enable easy "hijacking".
OTOH when I checked the arguments in gdb they looked always sane, up to
the last and crashing realloc() call. That's why I do not expect seeing
anything unusual there.
Valgrind did not see any bad free()s either.
> there can be some call abi issue (register clobbering,
> stack alignment,..) because of the asm, but that's hard
> to check.
Is musl in any way special compared to glibc/uclibc in its register usage?
> you may try tracing malloc calls (i don't know an easy
> way other than instrumenting musl, you can try python
> scripting gdb, the default gdb command language is not
> enough for reporting malloc args and return values).
This is something I wished to avoid. It does not promise much either,
but I may possibly try this if nothing else helps.
Thanks everyone for the help!
Rune
next prev parent reply other threads:[~2016-09-14 14:04 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-13 18:06 u-uy74
2016-09-13 19:20 ` Markus Wichmann
2016-09-13 20:41 ` Rich Felker
2016-09-13 20:43 ` Rich Felker
2016-09-14 10:32 ` u-uy74
2016-09-14 11:24 ` Szabolcs Nagy
2016-09-14 14:04 ` u-uy74 [this message]
2016-09-14 14:28 ` Rich Felker
2016-09-14 14:31 ` Timo Teras
2016-09-14 14:39 ` Rich Felker
2016-09-14 14:40 ` Rich Felker
2016-09-14 14:41 ` Szabolcs Nagy
2016-09-14 15:11 ` u-uy74
2016-10-02 10:59 ` "non-float" malloc (was: incompatibility between libtheora/mmx and musl) u-uy74
2016-10-02 11:17 ` u-uy74
2016-10-02 12:08 ` Szabolcs Nagy
2016-10-02 12:24 ` u-uy74
2016-10-02 13:24 ` u-uy74
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