Re: [PATCH v3] Implement /proc/pid/kill

[Eric W. Biederman]

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