[PATCH] utils: fix check_pid_path to work with deleted file as well

[Petr Štetiar]

Karel Kočí <karel.koci at nic.cz> [2020-07-02 12:49:56]:

Hi,

> check_pid_patch is checking if process with given PID and executable
> path is running. If this code fails the rest of the code can be
> convinced that program is no longer running and possibly spawns new
> instance that can collide with already running one. This behavior was
> reproduced with hostapd.
> 
> Symbolic link exe in process subdirectory in /proc points to original
> executable. The problem is that it reads as original path plus string
> ' (deleted)' if file is removed. The process is still running but
> original file is no longer available on files system.
> 
> This behavior is triggered not only when file is removed (unlinked) but
> also when file is replaced. This happens clearly on package update. In
> general this happens any time all references (hard links) to file are
> removed from file system.
> 
> This is not ultimate fix as exe link points to any last reference on
> file system with preference for original one. The problem is if there
> are multiple references and the original one is removed. This can be
> reproduced just by copying executable (hard linking) and unlinking the
> original one. In such case exe link would point to copy and not to
> original deleted one.

thanks, applied. Next time please send it with "[PATCH netifd] ..." subject as
otherwise it's not clear where to apply this.

-- ynezz