Re: procfs: boot- and runtime configurable access mode for /proc/<pid> dirs

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Mar 24, 2011 at 08:22:30PM +0200, Alexey Dobriyan wrote:
> On Thu, Mar 24, 2011 at 09:41:58AM +0100, Daniel Reichelt wrote:
> > > Keeping u/g/o inside kernel is horrible.
> > 
> > Why exactly? Since it's only a char and not char[] I don't see the
> > disadvantage over int or a define or whatever. Of course I could always
> > change that if that's a de-facto standard I just didn't know about.
> 
> Keep mode_t inside kernel, this will get rid of many ifdefs.
>  
> > > What is the usecase? Content of /proc/* is identical.
> > 
> > Use-case is to isolate process information from other users' or groups'
> > eyes, e.g. with 550 the output of ps aux only lists processes of the
> > groups your user is a member of.
> 
> This is doable with some ps(1) switch, I'm sure.
> 
> The content of /proc/$PID directory is not a secret.

More to the point, permissions in /proc/<pid>/* don't do us much good.
As the matter of fact, we ought to make them all flat - i.e. same for
user/group/other, since we have to recheck access rights on every damn
IO operations.  Checks done at open() are useless here - have the
task exec suid-root binary and they are obsolete.