[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20160914140450.GQ16436@example.net>
Date: Wed, 14 Sep 2016 16:04:50 +0200
From: u-uy74@...ey.se
To: musl@...ts.openwall.com
Subject: Re: incompatibility between libtheora/mmx and musl ?
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
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
