[linux-dvb] [PATCH] Bug in section filtering (and fix)

[Johannes Stezenbach]

Hi Mark,

just to let you know that this report and fix is highly appreciated,
but I simply am short of time and didn't have time to look into
the details to verify your fix. It won't drop off my TODO-list.

Would be cool if someone else had the time...

Johannes

On Thu, Sep 22, 2005 at 06:53:59PM +0100, Mark Adams wrote:
> There is a bug in dvb-core which causes large MPEG sections to be lost
> when they follow very small sections.
> 
> The problem happens when two sections begin in the same transport
> packet.  The dvb_demux code resets its buffer only before the first of
> these sections.  This means that when the second (or subsequent)
> section begins, there is up to 182 bytes of buffer space already used.
>  If the following section is close to the maximum size, it currently
> won't fit in the (4096-byte) buffer and is thrown away.
> 
> The fix is simply to enlarge the buffer by the size of one transport
> packet and correct one usage of the SECFEED_SIZE definition where what
> is really meant is the maximum size of a section.
> 
> I propose the following patch:
> 
> --- demux.h.orig	2005-03-02 07:37:55.000000000 +0000
> +++ demux.h	2005-09-21 18:41:10.000000000 +0100
> @@ -47,8 +47,11 @@
>   * DMX_MAX_SECFEED_SIZE: Maximum length (in bytes) of a private
> section feed filter.
>   */
> 
> +#ifndef DMX_MAX_SECTION_SIZE
> +#define DMX_MAX_SECTION_SIZE 4096
> +#endif
>  #ifndef DMX_MAX_SECFEED_SIZE
> -#define DMX_MAX_SECFEED_SIZE 4096
> +#define DMX_MAX_SECFEED_SIZE (DMX_MAX_SECTION_SIZE+188)
>  #endif
> 
> 
> --- dvb_demux.c.orig	2005-03-02 07:37:49.000000000 +0000
> +++ dvb_demux.c	2005-09-21 18:42:25.000000000 +0100
> @@ -302,7 +302,7 @@ static int dvb_dmx_swfilter_section_copy
>  	for(n = 0; sec->secbufp + 2 < limit; n++)
>  	{
>  		seclen = section_length(sec->secbuf);
> -		if(seclen <= 0 || seclen > DMX_MAX_SECFEED_SIZE
> +		if(seclen <= 0 || seclen > DMX_MAX_SECTION_SIZE
>  		   || seclen + sec->secbufp > limit)
>  			return 0;
>  		sec->seclen = seclen;
> 
> Signed-off-by: Mark Adams <mark147m at gmail.com>
> 
> Regards,
> 
> Mark
> 
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