linux-kernel - Re: [RFC] ps command race fix

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20060725105339.e8c25775.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 25 Jul 2006 10:53:39 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: [RFC] ps command race fix

On Mon, 24 Jul 2006 18:20:00 -0700
Andrew Morton <akpm@...l.org> wrote:
> 
> It allocates a potentially-significant amount of memory per-task, until
> that tasks exits (we could release it earlier, but the problem remains) and
> it adds yet another global lock in the process exit path.
> 
I see.

> >  5 files changed, 138 insertions(+), 62 deletions(-)
> 
> And it adds complexity and code.
> 
> So I think we're still seeking a solution to this.
> 
> Options might be:
> 
> a) Pin the most-recently-visited task in some manner, so that it is
>    still on the global task list when we return.  That's fairly simple to
>    do (defer the release_task()) but it affects task lifetime and visibility
>    in rare and worrisome ways.
> 
> b) Change proc_pid_readdir() so that it walks the pid_hash[] array
>    instead of the task list.  Need to do something clever when traversing
>    each bucket's list, but I'm not sure what ;) It's the same problem.
> 
>    Possibly what we could do here is to permit the task which is walking
>    /proc to pin a particular `struct pid': take a ref on it then when we
>    next start walking one of the pid_hash[] chains, we _know_ that the
>    `struct pid' which we're looking for will still be there.  Even if it
>    now refers to a departed process.
> 
> c) Nuke the pid_hash[], convert the whole thing to a radix-tree. 
>    They're super-simple to traverse.  Not sure what we'd index it by
>    though.
> 
> I guess b) is best.
> 

I tried b) at the first place. but it was not very good because 
proc_pid_readdir() has to traverse all pids, not tgids. So, I had to access
task_struct of the pid. I wanted to avoid to access task struct itself,
my patch implemented a table made only from tgids.

But as you say, my patch is much intrusive. 
I'll dig this more. thank you for advise.

Thanks,
-Kame




-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/