Re: shmctl(SHM_STAT) vs. /proc/sysvipc/shm permissions discrepancies

From: Michael Kerrisk (man-pages)
Date: Wed Dec 20 2017 - 11:18:12 EST

Hello Michal,

On 20 December 2017 at 10:20, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Tue 19-12-17 17:45:40, Michael Kerrisk wrote:
>> But, is
>> there a pressing reason to make the change? (Okay, I guess iterating
>> using *_STAT is nicer than parsing /proc/sysvipc/*.)
> The reporter of this issue claims that "Reading /proc/sysvipc/shm is way
> slower than executing the system call." I haven't checked that but I can
> imagine that /proc/sysvipc/shm can take quite some time when there are
> _many_ segments registered.

Yes, that makes sense.

> So they would like to use the syscall but
> the interacting parties do not have compatible permissions.

So, I don't think there is any security issue, since the same info is
available in /proc/sysvipc/*. The only question would be whether
change in the *_STAT behavior might surprise some applications into
behaving differently. I presume the chances of that are low, but if it
was a concert, one could add new shmctl/msgctl/semctl *_STAT_ALL (or
some such) operations that have the desired behavior.



Michael Kerrisk
Linux man-pages maintainer;
Linux/UNIX System Programming Training: