Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes

From: Kay Sievers
Date: Fri Mar 05 2010 - 13:52:12 EST

On Thu, Mar 4, 2010 at 14:14, Roland McGrath <roland@xxxxxxxxxx> wrote:
>> Security. This is beyond my understanding, hopefully the cc'ed
>> experts can help.
> There are a few different aspects of behavior change to think about.
> 1. Who can get a SIGCHLD and wait result they weren't expecting.
> 2. Who sees some PID for getppid() when they are expecting 1.
> 3. What ps shows.
> When I start thinking through what might be security issues, they are
> almost all #1 questions. ÂThere is a hairy nest of many variations of #1
> questions. ÂThe #2 question is pretty simple, but it also could be an issue
> for security when setuid is involved (or just correctness for any
> application).
> My impression is that #3 is the only actual motivation for this feature.
> So perhaps we should consider an approach that leaves the rest of the
> semantics alone and only affects that.

Oh, no. Actually getting the SIGCHILD is the needed feature here. A
process who sets the ANCHOR flag is surely expected to handle these
signals. It's all about a user "init-like" process" that can do
similar things for a logged-in user what /sbin/init can to for the
system. So, it's all about 1.), and 3.) is a nice side-effect, but not
the motivation to do this.

And 2.) is just very broken behavior that should be fixed in the
application, and it can be worked around in the sub-init process if

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