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SubjectRe: [PATCH] add umask parameter to procfs
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Herbert Poetzl <herbert@13thfloor.at> wrote:
> On Thu, Feb 17, 2005 at 03:41:19PM -0800, Andrew Morton wrote:
>> Rene Scharfe <rene.scharfe@lsrfire.ath.cx> wrote:

>> > Add proc.umask kernel parameter. It can be used to restrict permissions
>> > on the numerical directories in the root of a proc filesystem, i.e. the
>> > directories containing process specific information.
>> >
>> > E.g. add proc.umask=077 to your kernel command line and all users except
>> > root can only see their own process details (like command line
>> > parameters) with ps or top. It can be useful to add a bit of privacy to
>> > multi-user servers.

>> The feature seems fairly obscure, although very simple.
>> Is anyone actually likely to use this?

I'm using a openwall-patched kernel on some of my boxes with a similar
feature. I did not yet test this patch, but I like it. It's cheap, and
it fixes a potential security leak.

> what about parents (and especially the init process)
> some tools like pstree (or ps in certain cases) depend
> on their visibility/accessability ...

pstree will break if /proc/1 isn't readable, unless you specify a readable
starting pid. Since this is not the default case, this is IMO ok. (It should
be easy to rewrite it to trace the ppid-chains like "ps auxf" already does
correctly, or rather implement it in ps where it belongs).

None of my other tools seemed to stop working in an unintended way, but I
don't usurally spend my time watching processes.

Sample output of "ps auxf" on a openwall-patched system:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
7eggert 22504 5.0 3.5 2800 1608 pts/4 S 04:14 0:00 -bash
7eggert 22522 0.0 1.7 2856 792 pts/4 R 04:14 0:00 \_ ps auxf
7eggert 22483 2.3 3.4 2800 1588 pts/2 S 04:14 0:00 -bash

> what if you want to change it afterwards (when tools
> did break)?

Change the kernel command line back and reboot (or reload the module).

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