Package: libvorbisfile3
Version: 1.3.4-2
Severity: important
ov_pcm_seek wrongly returns OV_EOF or segfaults sometimes. I've
observed it in some situations, below is a very simple one to
reproduce. It's an important problem to me, because (unless fixed or
you can tell me exactly when seeking will work), I'd have to treat
all Ogg/Vorbis files as unseekable in my code, which would be a huge
performance penalty (decoding sequentially and buffering all in
memory).
% cat test.c
#include <stdio.h>
#include <vorbis/vorbisfile.h>
int main ()
{
OggVorbis_File vf;
fprintf (stderr, "%i\n", ov_fopen ("foo.ogg", &vf));
fprintf (stderr, "%i\n", ov_pcm_seek (&vf, 0));
fprintf (stderr, "%i\n", ov_pcm_seek (&vf, 0));
return 0;
}
% head -c 100000 /dev/zero|oggenc -Q -r - -o foo.ogg&& gcc -g test.c
-lvorbisfile && ./a.out
On i386:
0
0
-2
On amd64:
0
0
Segmentation fault
I tried to debug it and found: The 2nd time ov_pcm_seek_is_called
(from the 2nd ov_pcm_seek call), at line 1461
if(bisect!=vf->offset){
result=_seek_helper(vf,bisect);
if(result) goto seek_error;
}
begin == 3997 and vf->offset == 3997, so the call to _seek_helper is
skipped. However, ftell((FILE*)vf->datasource) == 4076, so it goes
on with a wrong file position, so _get_next_page fails and og
remains unintialized and ogg_page_serialno(&og) (line 1554) results
in UB.
I don't really understand the code: Telling from this line,
vf->offset should reflect the actual position of the data source.
But if so, I'd expect it to be adjusted after each successfull call
of seek_func (that's correctly done) and read_func. read_func is
only called from _get_data, but it doesn't adjust vf->offset.
Instead it puts the data into an internal buffer AFAIUI, so the
users of the data from the buffer are probably responsible for
adjusting vf->offset, but apparently something goes wrong there.
If I just set vf->offset to 4076 before line 1461 (2nd time), it
continues correctly. That's of course, not a fix, just an indication
that the wrong value of vf->offset is the real problem here.
Maybe vf->offset just needs to be revalidated before line 1461, but
it's used in many places, and I don't know how many of them might be
affected too.
-- System Information:
Debian Release: 8.4
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500,
'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 3.16.0-4-amd64 (SMP w/8 CPU cores)
Locale: LANG=de_DE, LC_CTYPE=de_DE (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages libvorbisfile3:amd64 depends on:
ii libc6 2.19-18+deb8u4
ii libogg0 1.3.2-1
ii libvorbis0a 1.3.4-2
ii multiarch-support 2.19-18+deb8u4
libvorbisfile3:amd64 recommends no packages.
libvorbisfile3:amd64 suggests no packages.
-- no debconf information
