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Bug 641128 - memmem, strstr, and strcasestr are broken
Summary: memmem, strstr, and strcasestr are broken
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: glibc
Version: 6.0
Hardware: All
OS: Linux
urgent
urgent
Target Milestone: rc
: ---
Assignee: Andreas Schwab
QA Contact: qe-baseos-tools-bugs
URL:
Whiteboard:
Depends On: 641124
Blocks: 643341
TreeView+ depends on / blocked
 
Reported: 2010-10-07 19:31 UTC by Jakub Jelinek
Modified: 2016-11-24 15:45 UTC (History)
9 users (show)

Fixed In Version: glibc-2.12-1.8.el6
Doc Type: Bug Fix
Doc Text:
Previously, the generic implementation of the strstr() and memmem() functions did not handle certain periodic patterns correctly and could find a false positive match. This error has been fixed, and both functions now work as expected.
Clone Of: 641124
Environment:
Last Closed: 2011-05-19 13:15:54 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2011:0584 0 normal SHIPPED_LIVE glibc bug fix and enhancement update 2011-05-18 17:56:51 UTC

Description Jakub Jelinek 2010-10-07 19:31:53 UTC 
+++ This bug was initially created as a clone of Bug #641124 +++

Description of problem:
glibc 2.9 through 2.12 have a bug in string searching algorithms which was just recently fixed upstream (note that glibc 2.11 introduced a replacement strstr for SSE4.2 platforms that avoids the bug on strstr and strcasestr, but at the expense of using a quadratic implementation instead of a linear version).  Since this bug can be triggered in any number of other packages, the upstream patch should be backported into the Fedora version of glibc.  http://sourceware.org/bugzilla/show_bug.cgi?id=12092

Version-Release number of selected component (if applicable):
glibc-2.12.1-2.x86_64
glibc-2.12.1-2.i686

How reproducible:
100% reproducible on problematic search patterns.  However, a machine with SSE4.2 hides the problem unless you use memmem.  Also, the problematic search patterns are not necessarily typical searches: the needle has to be periodic and at least 32 bytes, and the haystack has to match in most but not all of the periods of the needle to trigger the false positive match; so packages that use strstr() on hard-coded needles rather than on arbitrary user input are most likely immune.

Steps to Reproduce:
1. This demonstrates an example of existing packages that use strstr() on arbitrary input, and uses a shorter input string than the one listed in the glibc bug report.  First, validate that this machine is not using SSE4.2:
grep sse4_2 /proc/cpuinfo | wc -l
2. echo 'index(
;:11-:12-:12-:12-:12-:12-:12-:12-:12.:12.:12.:12.:12.:12.:12.:12.:12-,
:12-:12-:12-:12-:12-:12-:12-:12-)' | m4
  
Actual results:
1. 0
2. 37

Expected results:
1. 0
2.-1

Additional info:
Comment 5 Jaromir Hradilek 2010-10-15 14:20:16 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
Previously, the generic implementation of the strstr() and memmem() functions did not handle certain periodic patterns correctly and failed to find a match. This error has been fixed, and both functions now work as expected.
Comment 6 Eric Blake 2010-10-15 14:26:18 UTC 
The bug was false positive matches, not false negatives.  I updated the technical note accordingly.
Comment 7 Eric Blake 2010-10-15 14:26:18 UTC 
    Technical note updated. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    Diffed Contents:
@@ -1 +1 @@
-Previously, the generic implementation of the strstr() and memmem() functions did not handle certain periodic patterns correctly and failed to find a match. This error has been fixed, and both functions now work as expected.+Previously, the generic implementation of the strstr() and memmem() functions did not handle certain periodic patterns correctly and could find a false positive match. This error has been fixed, and both functions now work as expected.
Comment 10 errata-xmlrpc 2011-05-19 13:15:54 UTC 
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 therefore 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/RHBA-2011-0584.html
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