[PATCH] Mp4: fixed setting wrong mdat atom size in very rarecases.

[Maxim Dounin]

Hello!

On Tue, Nov 22, 2016 at 02:13:11PM +0800, 胡聪 (hucc) wrote:

> Hi,
> 
> On Tue, Nov 22, 2016 at 4:37 AM +0300, Valentin V. Bartenev wrote:
> 
> >On Monday 21 November 2016 23:10:25 胡聪 wrote:
> >
> >> -    if ((uint64_t) atom_data_size > (uint64_t) 0xffffffff) {
> >> +    if ((uint64_t) atom_data_size + sizeof(ngx_mp4_atom_header_t)
> >> +            > (uint64_t) 0xffffffff)
> >> +    {
> >>          atom_size = 1;
> >
> >Maxim wrote the expression the way that almost all compilers should optimize
> >it to comparison with one static constant.  I'm not sure about your case.
> 
> Yes, that is a matter. I checked that the above situation does not seem to be
> optimized.
> 
> # HG changeset patch
> # User hucongcong <hucong.c at foxmail.com>
> # Date 1479793208 -28800
> #      Tue Nov 22 13:40:08 2016 +0800
> # Node ID 7a4d011601cefeda16c8de2630ae0cc7639edf84
> # Parent  2c7a2d75938a31044552b0a6cd6edaebdaf0bd69
> Mp4: fixed setting wrong mdat atom size in very rare cases.
> 
> Atom size is the sum of atom header size and atom data size. The
> specification says that the first 4 bytes are set to one when
> the atom size is greater than the maximum unsigned 32-bit value.
> Which means atom header size should be considered when the
> comparison takes place between atom data size and 0xffffffff.
> 
> diff -r 2c7a2d75938a -r 7a4d011601ce src/http/modules/ngx_http_mp4_module.c
> --- a/src/http/modules/ngx_http_mp4_module.c	Mon Nov 21 16:49:19 2016 +0300
> +++ b/src/http/modules/ngx_http_mp4_module.c	Tue Nov 22 13:40:08 2016 +0800
> @@ -1229,7 +1229,9 @@ ngx_http_mp4_update_mdat_atom(ngx_http_m
>  
>      atom_header = mp4->mdat_atom_header;
>  
> -    if ((uint64_t) atom_data_size > (uint64_t) 0xffffffff) {
> +    if ((uint64_t) atom_data_size
> +        > (uint64_t) 0xffffffff - sizeof(ngx_mp4_atom_header_t))
> +    {
>          atom_size = 1;
>          atom_header_size = sizeof(ngx_mp4_atom_header64_t);
>          ngx_mp4_set_64value(atom_header + sizeof(ngx_mp4_atom_header_t),

Committed, thanks.

-- 
Maxim Dounin
http://nginx.org/