Re: [PATCH 1/2] break out page allocation warning code

[David Rientjes <rientjes@google.com>]

On Wed, 20 Apr 2011, KOSAKI Motohiro wrote:

> > That was true a while ago, but you now need to protect every thread's 
> > ->comm with get_task_comm() or ensuring task_lock() is held to protect 
> > against /proc/pid/comm which can change other thread's ->comm.  That was 
> > different before when prctl(PR_SET_NAME) would only operate on current, so 
> > no lock was needed when reading current->comm.
> 
> Right. /proc/pid/comm is evil. We have to fix it. otherwise we need change
> all of current->comm user. It's very lots!
> 

Fixing it in this case would be removing it and only allowing it for 
current via the usual prctl() :)  The code was introduced in 4614a696bd1c 
(procfs: allow threads to rename siblings via /proc/pid/tasks/tid/comm) in 
December 2009 and seems to originally be meant for debugging.  We simply 
can't continue to let it modify any thread's ->comm unless we change the 
over 300 current->comm deferences in the kernel.

I'd prefer that we remove /proc/pid/comm entirely or at least prevent 
writing to it unless CONFIG_EXPERT.

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