[mythtv-users] recent mythbackend crashing

Klaas de Waal klaas.de.waal at gmail.com
Sat Jun 18 05:56:47 UTC 2022


On Sat, 18 Jun 2022 at 03:33, Eyal Lebedinsky <eyal at eyal.emu.id.au> wrote:

> This issue is now tracked on bugzilla as
>         https://bugzilla.rpmfusion.org/show_bug.cgi?id=6327
>
> On 30/05/2022 11.00, Eyal Lebedinsky wrote:
> > Running f34 up-to-date.
> >
> > Recently, following an update of mythtv and the kernel, mythbackend
> started crahing even when not recording or watching.
> > Does anyone else see this?
>
>
> Interesting, this is not the same error but definitely related. The
previous bug was about parsing the header and extending one byte beyond the
header into the payload and this looks like it is accessing one byte beyond
the payload. If you do not get the previous error anymore this means that
the fix did work. Which I was not 100% sure about because I could not
reproduce the issue.
As with the previous bug, this now shows up because (1) somebody changed
the C-style arrays to C++-style std::arrays and (2) it looks like that in
your rpmfusion build there is array boundary checking enabled on std::array
accesses and (3) the streams that you encounter are composed so that this
does happen.
It is not usual to do array boundary checking on this code level because of
performance reasons; this code is executed for every 188 byte packet that
is received and I leave the math for you how many packets per second this
can be for 40 Mbit/s satellite transport stream.
I will have a look at it.

Klaas.
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