Bug 156029 - kernel may oops if more than 4k worth of string data returned in /proc/devices
kernel may oops if more than 4k worth of string data returned in /proc/devices
Status: CLOSED ERRATA
Product: Red Hat Enterprise Linux 2.1
Classification: Red Hat
Component: kernel (Show other bugs)
2.1
All Linux
medium Severity medium
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Assigned To: Don Howard
Brian Brock
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Depends On:
Blocks: 143573
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Reported: 2005-04-26 15:00 EDT by Neil Horman
Modified: 2007-11-30 17:06 EST (History)
1 user (show)

See Also:
Fixed In Version: RHSA-2007-0013
Doc Type: Bug Fix
Doc Text:
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Last Closed: 2007-01-17 05:14:35 EST
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RHEL 7.3 requirements from Atomic Host:
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Attachments (Terms of Use)
patch to add missing length check to /proc/devices file (1.58 KB, patch)
2005-04-26 15:00 EDT, Neil Horman
no flags Details | Diff

  None (edit)
Description Neil Horman 2005-04-26 15:00:40 EDT
Description of problem:
the read routine for /proc/devices is missing a length check routine. 
Consequently, if the number of block and char devices in a system totals more
than 4096 bytes of string data between their names and major/minor numbers, the
read routine will sprintf the data off the end of the page and oops the kernel.
other proc files that are part of proc_misc.c protect against this with a length
check that truncates the file if it goes over a page, but this check is missing
from get_device_list and get_blkdev_list.

Version-Release number of selected component (if applicable):
all

How reproducible:
always

Steps to Reproduce:
1. register sufficient char/block devices in a system to create > 4096 bytes of
string data for /proc/devices
2. cat /proc/devices
3.
  
Actual results:
system will oops on a page fault

Expected results:
system should truncate file to 4096 bytes.

Additional info:
Comment 1 Neil Horman 2005-04-26 15:00:40 EDT
Created attachment 113681 [details]
patch to add missing length check to /proc/devices file
Comment 5 Don Howard 2006-09-14 14:14:33 EDT
Hi Neil -

This ticket fell off my radar.  It looks like the RHEL3 patch applies to 2.1. 
Can you attach a test case for this issue?
Comment 6 Neil Horman 2006-09-14 15:14:30 EDT
hey don-
   I don't think I have my old test case laying about any more, but suffice it
to say, all you need to do is write a kernel module that calls register_chrdev
for 256 different major/minor combinations, and give each device a name that is
at least 20 characters long.  That will overrun the 4k buffer that is allocated
for /proc/devices and cause an oops.  with the patch the file will be truncated
at 4096 bytes.  

I'll see if I can throw my old test code back together in a little bit.
Comment 7 Don Howard 2006-09-14 15:30:09 EDT
Thanks for checking, Neil.  Don't worry about re-creating your testcase, I can
do that.  
Comment 11 Mike Gahagan 2006-12-19 15:15:38 EST
bug reproduced using e.70 and fix verified on e.71.

Comment 13 Red Hat Bugzilla 2007-01-17 05:14:35 EST
An advisory 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-2007-0013.html

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