Ubuntu
eglibc package

libc6 2.11.1-0ubuntu5 strcmp-ssse3 may return incorrect result

Bug #563291 reported by Yang Yu on 2010-04-14

This bug affects 3 people

Affects		Status	Importance	Assigned to	Milestone
	eglibc (Ubuntu)	Fix Released	High	Unassigned	Ubuntu ubuntu-10.04
	Lucid	Fix Released	High	Unassigned	Ubuntu ubuntu-10.04

Bug Description

Description: Ubuntu lucid (development branch)
Release: 10.04
libc6: Installed: 2.11.1-0ubuntu5

Using strncmp in my program. Sometimes it returns non-zero for identical portion of two strings. A following memcmp does return zero. The strncmp has strcmp-ssse3 implementation.

The bug only happens with certain addresses where the strings are stored, so most likely it is some alignment issue within strcmp-ssse3. If copying the un-matched strings to other buffers, the comparison usually succeed.

See the attached test program strcmp-ssse3-err.c. It has two strings stored at specific addresses which make strncmp fail.

Related branches

lp:ubuntu/lucid/eglibc

Revision history for this message

Yang Yu (yang-yyu) wrote on 2010-04-14:

A test program in which strncmp fails but memcmp succeeds Edit (1.6 KiB, text/plain)

Revision history for this message

Yang Yu (yang-yyu) wrote on 2010-04-14:

Note in this test program, the failure starts from the 48th characters.

Matthias Klose (doko) on 2010-04-14

Changed in eglibc (Ubuntu):
importance:	Undecided → High
status:	New → Confirmed

Matthias Klose (doko) on 2010-04-15

Changed in eglibc (Ubuntu):
milestone:	none → ubuntu-10.04
status:	Confirmed → In Progress

Matthias Klose (doko) on 2010-04-15

Changed in eglibc (Ubuntu Lucid):
status:	In Progress → Fix Committed

Revision history for this message

Matthias Klose (doko) wrote on 2010-04-16:

prepared a test package at
deb http://ppa.launchpad.net/ubuntu-toolchain/ppa/ubuntu lucid main

please could you check if the issue is fixed for you?

Revision history for this message

Yang Yu (yang-yyu) wrote on 2010-04-16:

Thanks for fixing it so quickly. I don't have access to the machine with the issue now. Will give it a try tomorrow.

Revision history for this message

Yang Yu (yang-yyu) wrote on 2010-04-17:

One of us tried the fix and it worked well. Thanks.

Revision history for this message

Launchpad Janitor (janitor) wrote on 2010-04-17:

This bug was fixed in the package eglibc - 2.11.1-0ubuntu6

---------------
eglibc (2.11.1-0ubuntu6) lucid; urgency=low

[ Kees Cook ]
* [BZ #11333], Handle unnecessary padding in getdents64. LP: #392501.

  [ Matthias Klose ]
  * Apply from the 2.11-x86 branch:
    - Fix bugs in strcmp-sse4.S and strcmp-ssse3.S (H.J. Lu). LP: #563291.
    - Fix bugs in memcpy-ssse3. LP: #560135.
  * Assign global scope to RFC 1918 addresses in getaddrinfo(). Thanks
    Tore Anderson. LP: #555210.
  * Re-enable the local-ipv6-lookup patch. Addresses #417757.
-- Matthias Klose <email address hidden> Sun, 18 Apr 2010 00:05:05 +0200