linux-kernel - Re: [PATCH] set*uid() must not fail-and-return on OOM/rlimits

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Message-ID: <20060820161739.GI602@1wt.eu>
Date:	Sun, 20 Aug 2006 18:17:39 +0200
From:	Willy Tarreau <w@....eu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Solar Designer <solar@...nwall.com>,
	Alex Riesen <fork0@...rs.sourceforge.net>,
	Willy Tarreau <wtarreau@...a.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] set*uid() must not fail-and-return on OOM/rlimits

On Sun, Aug 20, 2006 at 05:53:22PM +0200, Arjan van de Ven wrote:
> On Sun, 2006-08-20 at 19:30 +0400, Solar Designer wrote:
> > On Sun, Aug 20, 2006 at 12:07:06PM +0200, Alex Riesen wrote:
> > > Solar Designer, Sun, Aug 20, 2006 02:38:40 +0200:
> > > > Attached is a trivial patch (extracted from 2.4.33-ow1) that makes
> > > > set*uid() kill the current process rather than proceed with -EAGAIN when
> > > > the kernel is running out of memory.  Apparently, alloc_uid() can't fail
> > > > and return anyway due to properties of the allocator, in which case the
> > > > patch does not change a thing.  But better safe than sorry.
> > > 
> > > Why not ENOMEM?
> > 
> > ENOMEM would not be any better than EAGAIN from the security standpoint.
> > 
> > The problem is that there are lots of privileged userspace programs that
> > do not bother to check the return value from set*uid() calls (or
> > otherwise check that the calls succeeded) before proceeding with work
> > that is only safe to do with the *uid switched as intended.
> 
> sounds like a good argument to get the setuid functions marked
> __must_check in glibc...

Agreed, as I'm sure that I've not always checked it in some of my own
programs. A warning would have helped.

Willy

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