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Bug 459468

Summary:	kernel: binfmt_misc.c: avoid potential kernel stack overflow [rhel-3.9]
Product:	Red Hat Enterprise Linux 3	Reporter:	Eugene Teo (Security Response) <eteo>
Component:	kernel	Assignee:	Don Howard <dhoward>
Status:	CLOSED WONTFIX	QA Contact:	Martin Jenner <mjenner>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	3.9	CC:	dhoward, lwang
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2008-08-20 16:19:56 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	459462
Bug Blocks:

Description Eugene Teo (Security Response) 2008-08-19 07:38:52 UTC

+++ This bug was initially created as a clone of Bug #459462 +++

Description of problem:
Register the ":text:E::txt::/root/cat.txt:' rule in binfmt_misc (by root) and try launching the cat.txt file (by anyone) :) The result is - the endless recursion in the load_misc_binary -> open_exec -> load_misc_binary chain and stack overflow.

There's a similar problem with binfmt_script, and there's a sh_bang memner on linux_binprm structure to handle this, but simply raising this in binfmt_misc may break some setups when the interpreter of some misc binaries is a script.

So the proposal is to turn sh_bang into a bit, add a new one (the misc_bang) and raise it in load_misc_binary.  After this, even if we set up the misc -> script -> misc loop for binfmts one of them will step on its own bang and exit.

Note that this can be triggered with root help only.

http://lkml.org/lkml/2008/3/13/245

--- Additional comment from eteo on 2008-08-19 03:17:02 EDT ---

Proposed upstream patch:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3a2e7f47d71e1df86acc1dda6826890b6546a4e1

--- Additional comment from eteo on 2008-08-19 03:17:35 EDT ---

(In reply to comment #1)
> Proposed upstream patch:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3a2e7f47d71e1df86acc1dda6826890b6546a4e1

Note that there is a regression. See http://lkml.org/lkml/2008/8/18/544. The patch is not in upstream yet AFAIK.

Comment 1 Eugene Teo (Security Response) 2008-08-19 07:50:16 UTC

Steps to Reproduce:
1. as root user, run echo ":text:E::txt::/cat.txt:" >
/proc/sys/fs/binfmt_misc/register; touch /cat.txt; chmod +x /cat.txt
2) as normal user, run /cat.txt

Comment 3 Don Howard 2008-08-20 16:19:56 UTC

I can confirm that this reproducible on rhel3.

However, it doesn't rise to the level of critical bugfix, given that root-owned files must be mis-configured.