linux-kernel - Re: New Security Features, Please Comment

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Message-ID: <49362D1E.1000907@davidnewall.com>
Date:	Wed, 03 Dec 2008 17:24:22 +1030
From:	David Newall <davidn@...idnewall.com>
To:	Geoffrey McRae <geoff@...idhost.com>
CC:	Peter Teoh <htmldeveloper@...il.com>, Valdis.Kletnieks@...edu,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: New Security Features, Please Comment

Geoffrey McRae wrote:
> Right now the only forseeable problem is that if a process holds a fd
> open when the parent app changes its uid/gid, which still, the worst
> that it can do is read/write another user's file.

Well,  no, there are more problems than open file descriptors; and the
worst is much worse than reading or writing another user's file. 
Suppose you're changing the ids of the Perl, Python or PHP interpreter:
the first user could install a SIGCLD handler and fork and exec sleep. 
When sleep dies, the handler gets executed as another user - hopefully a
user with access to credit card details, or other financially valuable
information.
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