[Bug 2043711] Re: Open3.pm tries to run code in /tmp when updating ubuntu-drivers-common

[Andrew J. Caines]

You are of course quite right that the risk associated with a file
created with a "random" six character case-insensitive alphanumeric
suffix and run a moment later is far smaller than more obviously risky
misuses of /tmp. Nevertheless the issue is not about evaluating the risk
of an adversary creating over forty-four milliard files or symlinks per
package in /tmp, or if the code checks for the presence of the file
before trying to create it (which I trust it does), or just how random
the suffix really is, or how many race conditions might exist, or any of
the other cases we've seen exploited over the decades, but that this is
even a matter to consider in late 2024.

Since you mention it specifically, creating the file with mode 600 will
(or certainly should) of course prevent the contents of the file from
being overwritten by another user between creation and execution.

I consider it uncontroversial to claim that a standard process for updating software on Ubuntu should not
1) involve creating executables (or files containing code to be executed) directly in /tmp and running them as root, and
2) result in errors when /tmp is mounted noexec, especially when they may indicate unhandled breakage.

I briefly observed more similar errors during an update earlier today,
but was not quick enough to capture more details before the Software
Updater output window disappeared; however I doubt those details
provided any more useful information.

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https://bugs.launchpad.net/bugs/2043711

Title:
  Open3.pm tries to run code in /tmp when updating ubuntu-drivers-common

Status in perl package in Ubuntu:
  Invalid

Bug description:
  During update of ubuntu-drivers-common:

    Can't exec "/tmp/ubuntu-drivers-common.config.55GJ8b": Permission denied at /usr/lib/x86_64-linux-gnu/perl-base/IPC/Open3.pm line 178, <GEN0> line 1.
  open2: exec of /tmp/ubuntu-drivers-common.config.55GJ8b configure 1:0.9.6.2~0.22.04.4 failed: Permission 
    denied at /usr/share/perl5/Debconf/ConfModule.pm line 59.
    Preconfiguring packages ...
    Can't exec "/tmp/ubuntu-drivers-common.config.uSPrCH": Permission denied at /usr/lib/x86_64-linux-gnu/perl-base/IPC/Open3.pm line 178, <GEN0> line 1.
    open2: exec of /tmp/ubuntu-drivers-common.config.uSPrCH configure 1:0.9.6.2~0.22.04.4 failed: Permission 
    denied at /usr/share/perl5/Debconf/ConfModule.pm line 59.

  /tmp is mounted with noexec because running code from /tmp has been a
  vulnerability vector for several decades, hence reporting this as a
  vulnerability in perl-base.

  This error did not appear to prevent the update of ubuntu-drivers-
  common and "dpkg --verify ubuntu-drivers-common" returns 0.

  ___________________________________________________________________________________________________________

  Attempting to use the package search on this form by clicking the 🔍
  created a modal in which there is an error

    Sorry, something went wrong with your search. We've recorded what
  happened, and we'll fix it as soon as possible. (Error ID:
  OOPS-c80f71590b02908a1187b9f743c53eac)

  which is repeated with any attempt to search for a package.

  ___________________________________________________________________________________________________________

  Submitting this form gives an error

    "perl-base" does not exist in Ubuntu. Please choose a different
  package. If you're unsure, please select "I don't know"

    $ dpkg -S /usr/lib/x86_64-linux-gnu/perl-base/IPC/Open3.pm
    perl-base: /usr/lib/x86_64-linux-gnu/perl-base/IPC/Open3.pm
    $ dpkg -l perl-base
    Desired=Unknown/Install/Remove/Purge/Hold
    | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
    |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
    ||/ Name           Version           Architecture Description
    +++-==============-=================-============-=============================>
    ii  perl-base      5.34.0-3ubuntu1.2 amd64        minimal Perl system

  Looks like a package to me. Nevertheless, using "Did you mean..."
  offers "perl".

  ProblemType: Bug
  DistroRelease: Ubuntu 22.04
  Package: perl-base 5.34.0-3ubuntu1.2
  ProcVersionSignature: Ubuntu 6.5.0-1007.7-oem 6.5.3
  Uname: Linux 6.5.0-1007-oem x86_64
  ApportVersion: 2.20.11-0ubuntu82.5
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: ubuntu:GNOME
  Date: Thu Nov 16 10:08:48 2023
  InstallationDate: Installed on 2016-04-23 (2763 days ago)
  InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
  ProcEnviron:
   TERM=rxvt
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: perl
  UpgradeStatus: Upgraded to jammy on 2022-08-19 (453 days ago)

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