Forward: Bug#138975: hotplug: /tmp symlink vulnerability

[Fumitoshi UKAI <ukai@debian.or.jp>]

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Hi,

I received the following bug report.
It actually create any files on tye system by dangling symlinking
in /tmp/test.<number> (touch follows symlinks).

Anyway as report said, I think it's better to touch /tmp itself
instead of touch /tmp/test.$$ and remove it.  
If directory is writable, touch the directory will be success, otherwise
touch will be failed. 

How about this ?

Index: etc/hotplug/ieee1394.agent
===================================================================
RCS file: /cvsroot/linux-hotplug/admin/etc/hotplug/ieee1394.agent,v
retrieving revision 1.3
diff -u -u -r1.3 ieee1394.agent
--- etc/hotplug/ieee1394.agent	4 Jan 2002 18:39:49 -0000	1.3
+++ etc/hotplug/ieee1394.agent	19 Mar 2002 01:36:56 -0000
@@ -33,9 +33,9 @@
 
 # if called too early in booting, things break
 # (bash creates tempfiles)
-if touch /tmp/test.$$ >/dev/null 2>&1
+if touch /tmp >/dev/null 2>&1
 then
-	rm -f /tmp/test.$$
+	: ok
 else
 	mesg Need writable /tmp ...
 	exit 1

Regards,
Fumitoshi UKAI


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From: Zygo Blaxell <zblaxell@feedme.hungrycats.org>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: Bug#138975: hotplug: /tmp symlink vulnerability
Date: Mon, 18 Mar 2002 18:02:38 -0500
Message-ID: <E16n69G-00034f-00@satsuki.furryterror.org>

Package: hotplug
Version: 0.0.20020114-5
Severity: normal
File: /etc/hotplug/ieee1394.agent
Tags: security

Seen in /etc/hotplug/ieee1394.agent:

	if touch /tmp/test.$$ >/dev/null 2>&1
	then
		rm -f /tmp/test.$$
	else
		mesg Need writable /tmp ...
		exit 1
	fi

Not only does this follow symlinks when it executes as root, thereby allowing someone
to create files all over the system, but it also removes innocent files created
under /tmp whose names happen to coincide with the PID of the agent...

A better approach would be to try to create a directory under /tmp.
That won't work if the /tmp disk is full, but on the other hand not much is
going to work in such a state anyway.

An even better approach would be to try to touch /tmp itself--if that
fails, you certainly won't be able to write files in subdirectories
of /tmp.

-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux satsuki 2.4.18-pre7aa2-zb-p3-laptop #1 Sat Feb 9 17:03:54 EST 2002 i686
Locale: LANG=C, LC_CTYPE=

Versions of packages hotplug depends on:
ii  debconf                       1.0.26     Debian configuration management sy
ii  modutils                      2.4.13-3   Linux module utilities.