[Bug 1890006] Re: Hash mismatch on "apt update"

Sun Aug 2 19:33:22 UTC 2020

VT-x status in BIOS is a red herring. Turns out modern Virtualbox won't
even start VM's without VT-x.

A true cause turned out to be "Windows Sandbox" feature (although I
imagine for some other users the problem might be triggered by "Windows
Subsystem for Linux" or anti-virus software).

Here is how to reproduce it in Windows 10:

  1. Enable "Windows Sandbox" (Control panel -> Programs and Features -> Turn Windows features on or off)
  2. After restart run Ubuntu live ISO in virtualbox and notice that
    a) VM slows to a crawl, some apps (firefox) start crashing randomly, etc
    b) Virtualbox shows "green turtle" icon (third from the right on the lower panel) which lists Execution engine as "native API" instead of "VT-x"
    c) Running "apt update" produces error mentioning "hash mismatch"
    d) Running workaround (mkdir -p /etc/gcrypt; echo intel-ssse3 > /etc/gcrypt/hwf.deny) fixes the apt error
  3. Disable "Windows Sandbox" feature
  4. After Windows restart run Ubuntu in Virtualbox and be surprised by green turtle still being there, all mentioned problems still present
  5. Restart Windows second time, run Ubuntu in Virtualbox again, this time there is a blue chip instead of green turtle and apt works without workarounds

Clearly it seems that gcrypt isnt at fault here and the true culprits
are Windows Sandbox (possibly some other mechanism that Windows Sandbox
enables) and/or Virtualbox. However the result is that new users are
getting wrong impression about GNU/Linux and Ubuntu in particular (it
appears slow and lags during "live" phase, fails to update after
install).

So I'd say Ubuntu should detect that it's being run in this broken
virtualization mode, show the informative explanation to user (that
their current experience isn't representative && how they can fix that)
or at least enable the workaround for gcrypt (although if SSSE3 is buggy
in this mode, I imagine more things are stealthily broken).

Surprisingly Ubuntu still finishes installation, even with default
"update from internet" option enabled. After installation, "apt update"
still produces the same "hash mismatch" errors though. Enabling
workaround and rerunning "apt update" predictably finds many more (292
right now) packages that are to be upgraded. This fail-open behavior
(installer and updater ignoring the errors) will no doubt lead to subtle
bug down the road for the users as well (I'd argue that it's a security
issue as well - users not being informed about security patches they're
missing).

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https://bugs.launchpad.net/bugs/1890006

Title:
  Hash mismatch on "apt update"

Status in apt package in Ubuntu:
  New

Bug description:
  This is a really weird bug that is happening on Ubuntu 20.04 LTS (Live
  ISO!!!) and Kali 2020.2, but not Debian 10 (so, it affects at least
  apt 2.0.2ubuntu0.1 and does not affect 1.8.2.1). It also only occurs
  on a single PC (as far as I know). All testing was done in Virtualbox
  and moving VM's to another PC fixed issue (without changing anything
  inside the VM).

  On running "apt update", there is an error "Hash Sum mismatch" which
  shows that SHA1 and SHA256 hashes differ from expected (while MD5 and
  file size is correct). E.g.:

    Hash Sum mismatch
    Hashes of expected file:
     - Filesize:314536 [weak]
     - SHA256:aa1c6c96b09a0c695dc475d99b407c675e564fbfe51b3e26230c6320b45666d0
     - SHA1:4f438d7e0c78dfb0486f86dc0a3dba30575eb617 [weak]
     - MD5Sum:5269212c54feb3dceabadb66583f6778 [weak]
    Hashes of received file:
     - SHA256:f47a968e7a10aff91df8b1d3f682ce11d161ff1b17056268b9ae1c10447523b2
     - SHA1:2839e062232ed234d0c04e60fe6b2a687c950e5b [weak]
     - MD5Sum:5269212c54feb3dceabadb66583f6778 [weak]
     - Filesize:314536 [weak]

  I ran packet capture and extracted archives which are getting
  verified. All of their hashes are correct (exactly as expected).

  It seems that calculating SHA1 and SHA256 the way APT does it produces
  wrong result, while running command line tools sha1sum and sha256sum
  (on the same PC inside the same VM) produces correct result.

  I wrote the minimal reproducible example (hashtest.cc) that produces
  output such as this:

  Calculating hashes same way apt does.

   - MD5Sum:c89b13b76197d0d554400e00e46c0740
   - SHA1:f6901a4486e69a1f503401daa02b520f1b0e22ba
   - SHA256:9075301b3961aca23b69bf2868a18dca184b383a0ec1de35516f0a8a182c2cb6
   - SHA512:7506f6f5c5d5e97f8c6ecac2489e7d6260002bd530370c6193a04620f94285dca0f5cf2bb9ead40afbd72fdf3a239349a57f81165b5b857af6ad7ddeab8da036
   - Checksum-FileSize:892549

  Calculating hashes through command line tools.

   - md5sum: c89b13b76197d0d554400e00e46c0740
   - sha1sum: f6901a4486e69a1f503401daa02b520f1b0e22ba
   - sha256sum: 9075301b3961aca23b69bf2868a18dca184b383a0ec1de35516f0a8a182c2cb6
   - sha512sum: 7506f6f5c5d5e97f8c6ecac2489e7d6260002bd530370c6193a04620f94285dca0f5cf2bb9ead40afbd72fdf3a239349a57f81165b5b857af6ad7ddeab8da036

  It's in the attachment alongside with an example file that causes this
  hash mismatch. There's also debug.log which contains various versions,
  etc (although as I said, it has been verified on latest Ubuntu Live
  ISO).

  I have a suspicion that the bug is in the gcrypt library, not apt itself, but I haven't yet verified it. The libgcrypt20 version in Ubuntu is 1.8.5-5ubuntu1 (in Kali as well), while Debian 10 (which isn't affected) uses 1.8.4-5.
  --- 
  ProblemType: Bug
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  CasperMD5CheckMismatches: ./casper/filesystem.squashfs
  CasperMD5CheckResult: fail
  CasperVersion: 1.445
  DistroRelease: Ubuntu 20.04
  LiveMediaBuild: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
  NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
  Package: apt 2.0.2
  PackageArchitecture: amd64
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
  Tags:  focal
  Uname: Linux 5.4.0-26-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:

  _MarkForUpload: True

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