[Bug 1756209] Re: i386 implementation of memmove broken since glibc 2.21

[Steve Langasek]

Hello Thomas, or anyone else affected,

Accepted glibc into bionic-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/glibc/2.27-3ubuntu1.3
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
bionic to verification-done-bionic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-bionic. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: glibc (Ubuntu Bionic)
       Status: Confirmed => Fix Committed

** Tags added: verification-needed verification-needed-bionic

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https://bugs.launchpad.net/bugs/1756209

Title:
  i386 implementation of memmove broken since glibc 2.21

Status in glibc package in Ubuntu:
  Fix Released
Status in glibc source package in Xenial:
  New
Status in glibc source package in Bionic:
  Fix Committed

Bug description:
  [Impact]
  * i386 memmove breaks when crossing the 2GB threshold.

  [Test Case]

  * Compile and run the reproducer as described at
  https://github.com/fingolfin/memmove-bug or observe string/test-
  memmove test passing during the build/autopkgtest on i386.

  [Regression Potential]

  * Can break memmove, but this is unlikely since memmove is the very
  function fixed by fixing signedness handling.

  [Original Bug Text]

  In glibc 2.21 they optimized i386 memcpy:

  https://sourceware.org/ml/libc-alpha/2015-02/msg00119.html

  The implementation contained a bug which causes memmove to break when
  crossing the 2GB threshold.

  This has been filed with glibc here (filed by someone else, but I have
  requested an update from them as well):

  https://sourceware.org/bugzilla/show_bug.cgi?id=22644

  Unfortunately they have not yet taken action on this bug, however I
  want to bring it to your attention in the hope that it can be patched
  into all current Ubuntu releases as soon as possible. I hope this is
  not improper procedure. Both myself and another (see comment 1 in the
  glibc bug report) have tested the patch provided in the above glibc
  bug report and it does appear to fix the problem, however I don't know
  what the procedure is for getting it properly confirmed/tested and
  merged into Ubuntu.

  As requested in the guidelines:

  1) We are using:
  Description:    Ubuntu 16.04.4 LTS
  Release:        16.04

  2)
  libc6:i386:
    Installed: 2.23-0ubuntu10

  However as stated above this has been present since libc6:i386 2.21
  and affects Ubuntu 15.04 onward. (I have actually tested this as well.
  15.04 conveniently used both glibc 2.19 and 2.21 so it was a good test
  platform when I was initially attempting to track down the problem.)

  3) What we expected to happen:
  memmove should move data within the entire valid address space without segfaulting or corrupting memory.

  4) What happened instead:
  When memmove attempts to move data crossing the 2GB threshold it either segfaults or causes memory corruption.

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