Date: Thu, 22 Sep 2011 21:57:54 +0400 From: Vasiliy Kulikov <segoon@...nwall.com> To: kernel-hardening@...ts.openwall.com, Andrew Morton <akpm@...ux-foundation.org> Cc: Cyrill Gorcunov <gorcunov@...il.com>, Al Viro <viro@...iv.linux.org.uk>, Christoph Lameter <cl@...ux-foundation.org>, Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH 1/2] proc: force dcache drop on unauthorized access Hello Andrew, On Sat, Sep 10, 2011 at 20:40 +0400, Vasiliy Kulikov wrote: > The patch "proc: fix races against execve() of /proc/PID/fd**" is still > a partial fix for a setxid problem. link(2) is a yet another way to > identify whether a specific fd is opened by a privileged process. By > calling link(2) against /proc/PID/fd/* an attacker may identify whether > the fd number is valid for PID by analysing link(2) return code. > > Both getattr() and link() can be used by the attacker iff the dentry is > present in the dcache. In this case ->lookup() is not called and the > only way to check ptrace permissions is either operation handler or > ->revalidate(). The easiest solution to prevent any unauthorized access > to /proc/PID/fd*/ files is to force the dentry drop on each unauthorized > access attempt. > > If an attacker keeps opened fd of /proc/PID/fd/ and dcache contains > a specific dentry for some /proc/PID/fd/XXX, any future attemp to use the > dentry by the attacker would lead to the dentry drop as a result of a > failed ptrace check in ->revalidate(). Then the attacker cannot spawn a > dentry for the specific fd number because of ptrace check in ->lookup(). > > The dentry drop can be still observed by an attacker by analysing > information from /proc/slabinfo, which is addressed in the successive > patch. After (almost) everybody agreed that closing slabinfo and similar is a good thing, should I resend these 2 patches (/proc/PID/fd and slabinfo) with sysfs addition or you'll take these patches and I'll send sysfs patch after them? Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments
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