[Bug 1890168] Re: shm_open() fails with EACCESS for root user

[Ubuntu Foundations Team Bug Bot]

** Package changed: ubuntu => glibc (Ubuntu)

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https://bugs.launchpad.net/bugs/1890168

Title:
  shm_open() fails with EACCESS for root user

Status in glibc package in Ubuntu:
  New

Bug description:
  In Ubuntu 20.04 I'm having problem with accessing shared memory
  segments by different users. The associated files are created using
  shm_open() with the combination of O_CREAT and O_RDWR flags and placed
  in /dev/shm. The example of such a code is in the enclosed source
  file.

  When I run it for the first time, it works as expected and
  /dev/shm/testshm is created:

  $ ls -la /dev/shm
  total 0
  drwxrwxrwt  2 root   root     60 Aug  3 16:34 .
  drwxr-xr-x 18 root   root   4580 Aug  3 12:41 ..
  -rw-rw-r--  1 krejci krejci    0 Aug  3 14:37 testshm

  Then running program again under the same user works fine, but when I
  try to run the program as root (or any other user), I'm getting
  "Permission denied":

  # id
  uid=0(root) gid=0(root) groups=0(root)
  # ./test
  return value -1
  result 13: Permission denied

  The example program works as expected on previous Ubuntu (18.04,
  19.10) releases as well as on other linux distros - other users has
  access according to the set permissions (root is always able to access
  it).

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: libc6 2.31-0ubuntu9
  ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
  Uname: Linux 5.4.0-42-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.4
  Architecture: amd64
  CasperMD5CheckResult: skip
  Date: Mon Aug  3 17:35:07 2020
  InstallationDate: Installed on 2020-08-03 (0 days ago)
  InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
  SourcePackage: glibc
  UpgradeStatus: No upgrade log present (probably fresh install)

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