Re: [PATCH v3] Implement /proc/pid/kill
From: Eric W. Biederman
Date: Sun Nov 11 2018 - 20:19:42 EST
David Laight <David.Laight@xxxxxxxxxx> writes:
> From: Daniel Colascione
>> Sent: 31 October 2018 19:33
> ...
>> You can't do it today with kill. The idea that keeping a open file
>> descriptor to a /proc/pid or a file within it prevents PID reuse is
>> widespread, but incorrect.
>
> Is there a real good reason why that shouldn't be the case?
> ie Holding a reference on the 'struct pid' being enough to stop reuse.
>
> A patch to do that would be more generally useful.
Holding an open file descriptor to /proc/pid is enough to prevent pid
reuse problems. If a pid number is reused a new 'struct pid' is
generated. There is not 'struct pid' reuse.
So in solving this the kernel data structure you would need to hold onto
is a 'struct pid'. It is just necessary to add an interface to sending
signals to that 'struct pid' and not looking up the 'struct pid' again
by number.
Eric