[FFmpeg-devel] [PATCH][RFC] nsv seeking

[Michael Niedermayer]

On Wed, Apr 22, 2009 at 12:27:20PM +0530, Jai Menon wrote:
> On Wed, Apr 22, 2009 at 5:10 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Apr 21, 2009 at 09:43:16PM +0530, Jai Menon wrote:
> >> On Mon, Apr 20, 2009 at 11:48 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Mon, Apr 20, 2009 at 08:03:40PM +0530, Jai Menon wrote:
> >> >> On Mon, Apr 20, 2009 at 6:24 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> >> > On Sun, Apr 19, 2009 at 04:46:48PM +0530, Jai Menon wrote:
> >> >> >> On 4/18/09, Fran?ois Revol <revol at free.fr> wrote:
> >> >> > [...]
> >> >> >> @@ -348,12 +349,22 @@ static int nsv_parse_NSVf_header(AVFormatContext *s, AVFormatParameters *ap)
> >> >> >> ? ? ?PRINT(("NSV got infos; filepos %"PRId64"\n", url_ftell(pb)));
> >> >> >>
> >> >> >> ? ? ?if (table_entries_used > 0) {
> >> >> >> + ? ? ? ?int i;
> >> >> >> ? ? ? ? ?nsv->index_entries = table_entries_used;
> >> >> >> ? ? ? ? ?if((unsigned)table_entries >= UINT_MAX / sizeof(uint32_t))
> >> >> >> ? ? ? ? ? ? ?return -1;
[...]
> >> >> >> + ? ? ? ?nsv->nsvs_file_offset = av_malloc((unsigned)table_entries_used * sizeof(uint32_t));
> >> >> >> +
> >> >> >> + ? ? ? ?for(i=0;i<table_entries_used;i++)
> >> >> >> + ? ? ? ? ? ?nsv->nsvs_file_offset[i] = get_le32(pb) + size;



> >> >> >
> >> >> > exploitable
> >> >>
> >> >> I can't think of any feasible attack vector here. Could you be a little verbose.
> >> >
> >> > table_entries_used * 4 overflows
> >>
> >> So you want the file offset table entries to be 64 bit?
> >
> > no i want you to make sure you allocate a table that is capable to
> > hold the number of entries you write into it
> 
> Sorry, I don't quite understand. There are table_entries_used no.of
> entries in the file offset table. And I'm writing exactly those amount
> to the buffer.

example:
table_entries_used= 0x4FFFFFFF

table_entries_used * sizeof(uint32_t) = 0x4FFFFFFF * 4 = 0x3FFFFFFC

nsv->nsvs_file_offset= av_malloc(0x3FFFFFFC)

for(i=0; i<0x4FFFFFFF; i++)
    write 4 bytes to nsv->nsvs_file_offset[i]

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The bravest are surely those who have the clearest vision
of what is before them, glory and danger alike, and yet
notwithstanding go out to meet it. -- Thucydides
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