Bug 70607 – Oops in get_filesystem_info due to lack of locking

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Bug 70607 - Oops in get_filesystem_info due to lack of locking

Summary:	Oops in get_filesystem_info due to lack of locking

Status:	CLOSED ERRATA

Aliases:	None

Product:	Red Hat Enterprise Linux 2.1
Classification:	Red Hat
Component:	kernel (Show other bugs)
Sub Component:
Version:	2.1
Hardware:	i686 Linux

Priority	medium Severity medium
Target Milestone:	---
Target Release:	---
Assigned To:	Stephen Tweedie
QA Contact:	Brian Brock
Docs Contact:

URL:
Whiteboard:
Keywords:

Depends On:
Blocks:	107565
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Reported:	2002-08-02 16:43 EDT by Tim Wright
Modified:	2007-11-30 17:06 EST (History)
CC List:	3 users (show)

See Also:
Fixed In Version:
Doc Type:	Bug Fix
Doc Text:
Story Points:	---
Clone Of:
Environment:
Last Closed:	2004-04-21 21:02:53 EDT
Type:	---
Regression:	---
Mount Type:	---
Documentation:	---
CRM:
Verified Versions:
Category:	---
oVirt Team:	---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---

Attachments	(Terms of Use)
Suggested patch (wrong line numbers but it applies). (879 bytes, patch) 2002-08-02 16:45 EDT, Tim Wright	no flags	Details \| Diff
Add an attachment (proposed patch, testcase, etc.)

External Trackers
Tracker	ID	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHSA-2004:105	normal	SHIPPED_LIVE	Moderate: kernel security update	2004-04-21 00:00:00 EDT

Groups: None (edit)

Description Tim Wright 2002-08-02 16:43:56 EDT

Description of Problem:
If multiple mounts/unmounts are occurring, and a process is accessing/reading
from /proc/mounts, it is possible for an oops to occur on an SMP machine. This
is because the vfsmntlist can change while we're navigating it, but the code
doesn't grab any locks to prevent this. If a vfsmount "p" is removed from the
list while we're in d_path(), then we'll follow an invalid "next" pointer on
return from d_path().

Version-Release number of selected component (if applicable):
Any of 2.4.9-e.3, e.5 and e.8 are susceptible.

How Reproducible:
100%.

Steps to Reproduce:
1. Start some processes mounting and unmounting filesystems in a loop.
2. Repeatedly 'cat /proc/mounts' or otherwise read it.
3. Wait for the oops.

Actual Results:
An oops happens.

Expected Results:
No oops :-)

Additional Information:
A suggested fix is to grab the dcache_lock which apparently protects vfsmntlist.
This seems reasonable since we only process one page worth of information.

Comment 1 Tim Wright 2002-08-02 16:45:23 EDT

Created attachment 68624 [details]
Suggested patch (wrong line numbers but it applies).

Comment 8 Jason Baron 2004-02-09 16:51:27 EST

patch applied to the U4 update stream. changing state to modified.
kernel is available at:

http://people.redhat.com/~jbaron/.private/u4/2.4.9-e.37.3.test/

Comment 9 John Flanagan 2004-04-21 21:02:54 EDT

An errata has been issued which should help the problem described in this bug report. 
This report is therefore being closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files, please follow the link below. You may reopen 
this bug report if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2004-105.html

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