linux-kernel - Re: PROBLEM?: "permission denied" when accessing /proc/self/fd/* after setuid

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Date:	Fri, 08 Aug 2008 11:54:48 +0930
From:	Daryl Tester <dt-lkml@...dcraftedcomputers.com.au>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	Sven Wegener <sven.wegener@...aler.net>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: PROBLEM?: "permission denied" when accessing /proc/self/fd/*
 after setuid

Alexey Dobriyan wrote:

> Something similar was fixed in 2.6.22, but let me check.

You're right - from <http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.22>:

commit 8948e11f450e6189a79e47d6051c3d5a0b98e3f3
Author: Alexey Dobriyan <adobriyan@...nvz.org>
Date:   Tue May 8 00:23:35 2007 -0700

    Allow access to /proc/$PID/fd after setuid()

    /proc/$PID/fd has r-x------ permissions, so if process does setuid(), it
    will not be able to access /proc/*/fd/. This breaks fstatat() emulation
    in glibc.

    open("foo", O_RDONLY|O_DIRECTORY)       = 4
    setuid32(65534)                         = 0
    stat64("/proc/self/fd/4/bar", 0xbfafb298) = -1 EACCES (Permission denied)


However, one of the kernels I tried this on (and failed) was a 2.6.24-19 -
is it possible this patch was backed out?

Cheers,
  --dt

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