linux-kernel - Re: [PATCH] binfmt_elf: core dump masking support

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Message-ID: <20061220154056.GA4261@ucw.cz>
Date:	Wed, 20 Dec 2006 15:40:56 +0000
From:	Pavel Machek <pavel@...e.cz>
To:	Andrew Morton <akpm@...l.org>
Cc:	"Kawai, Hidehiro" <hidehiro.kawai.ez@...achi.com>,
	linux-kernel@...r.kernel.org, gregkh@...e.de,
	james.bottomley@...eleye.com, Satoshi OSHIMA <soshima@...hat.com>,
	"Hideo AOKI@...hat" <haoki@...hat.com>,
	sugita <yumiko.sugita.yf@...achi.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] binfmt_elf: core dump masking support

Hi!

> > When a new process is created, the process inherits the coremask
> > setting from its parent. It is useful to set the coremask before
> > the program runs. For example:
> > 
> >   $ echo 1 > /proc/self/coremask
> >   $ ./some_program
> 
> The requirement makes sense, I guess.
> 
> Regarding the implementation: if we add
> 
> 	unsigned char coredump_omit_anon_memory:1;
> 
> into the mm_struct right next to `dumpable' then we avoid increasing the
> size of the mm_struct, and the code gets neater.
> 
> 
> Modification of this field is racy, and we don't have a suitable lock in
> mm_struct to fix that.  I don't think we care about that a lot, but it'd be
> best to find some way of fixing it.
> 
> 
> Really we should convert binfmt_aout.c and any other coredumpers too.
> 
> 
> Does this feature have any security implications?  For example, there might
> be system administration programs which force a coredump on a "bad"
> process, and leave the core somewhere for the administrator to look at. 
> With this change, we permit hiding of that corefile's anon memory from the
> administrator.  OK, lame example, but perhaps there are better ones.

User can already ulimit -c 0 on himself, perhaps we want to use same
interface here? ulimit -cmask=(bitmask)?
							Pavel
-- 
Thanks for all the (sleeping) penguins.
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