Re: [PATCH 1/1] Add poll method to mkiss let notify hangup to the user process.

[Jean-Christian de Rivaz <jc@eclis.ch>]

Le 03. 10. 15 02:29, David Ranch a écrit :
>
> Hello Jean-Christian, Everyone,
>
> Thanks for working on this as I'm pretty sure I've bit hit by this 
> panic as well though I wasn't able to reproduce it more readily. 
> Anyway, if this is the proper fix moving forward, will the kernel not 
> panic even if kissattach is not updated?

Hello David,

The kernel will still panic and crash the system. The patch purpose is 
only to allow hangup notification to the user space. It has the side 
effect to reduce the race window of the panic&crash only if the user 
application get the hangup notification and close the file descriptor. 
The window is reduced in that case, but the window still exists.

Even with this patch and the user space application patch, the kernel is 
still unsafe, as a packet can still reach the parasitic AX25 interface 
in the time between the kiss_open() in the kernel and the close() in the 
user application. More important, as I stated before, safety of the 
kernel cannot depend on a user space application closing a file 
descriptor. A fix to prevent mkiss_open() call on a removed serial 
device is still needed. I proposed patches and options, but to date I 
only get two critics and no hint on how to solve the problem. The tty 
maintainers stay silent.

> Can you also include the needed patch for the kissattach program to 
> complete this solution?

Yes, it was posted a few minutes before in the linux-hams mailing list 
only because it don't concern the kernel mailing list:

http://www.spinics.net/lists/linux-hams/msg03520.html

Jean-Christian
--
To unsubscribe from this list: send the line "unsubscribe linux-hams" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html