svn commit: r220526 - head/sys/kern

[Attilio Rao]

2011/4/15 Kostik Belousov <kostikbel at gmail.com>:
> On Fri, Apr 15, 2011 at 12:46:18PM -0400, Attilio Rao wrote:
>> 2011/4/15 Kostik Belousov <kostikbel at gmail.com>:
>> > On Thu, Apr 14, 2011 at 05:13:28PM -0400, John Baldwin wrote:
>> >> On Sunday, April 10, 2011 1:07:03 pm Konstantin Belousov wrote:
>> >> > Author: kib
>> >> > Date: Sun Apr 10 17:07:02 2011
>> >> > New Revision: 220526
>> >> > URL: http://svn.freebsd.org/changeset/base/220526
>> >> >
>> >> > Log:
>> >> >   Some callers of proc_reparent() already have the parent process locked.
>> >> >   Detect the situation and avoid process lock recursion.
>> >> >
>> >> >   Reported by:      Fabian Keil <freebsd-listen fabiankeil de>
>> >> >
>> >> > Modified:
>> >> >   head/sys/kern/kern_exit.c
>> >>
>> >> Can we instead assert it is always held and fix callers that don't?  Using
>> >> locked variables is messy and I'd rather avoid it when possible.  We already
>> >> require the caller to hold other locks for this operation.
>> >>
>> > I agree that this is ugly, and proper fix probably would be something else.
>> > E.g. struct proc could grow another field that holds a pointer to the ucred
>> > it is accounted for, and locked with some global lock.
>>
>> As you already hold allproc_lock the process can't be distructed, then
>> as I already pointed out to Tomasz, it should alright to just bump the
>> refcount for cred and pass down, I guess.
> I do not see how allproc_lock is useful there, unless setuid(2) and
> other syscalls, which change the process credentials, are protected by
> the same lock. The issue there is in accounting for wrong container.
> You want to avoid a race between dereferencing stale p_ucred and the
> process moving to another container.

I thought the issue was just prevent destroying of process/ucred I may
need to better look at callers then if you also want to avoid
credentials changes. BTW, a global lock for that is not what I really
hope to see.

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein