[Bug 2064685] Re: write says write: effective gid does not match group of /dev/pts/5

[Robert Dinse]

This does not really fix security because one aspect of security is
availability to legitimate users and this breaks the latter.  Seems
there are better ways to fix such as restricting what this can write to
with apparmor?  Or just fixing the coding so it does parse the input
more carefully.

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Title:
  write says write: effective gid does not match group of /dev/pts/5

Status in util-linux package in Ubuntu:
  Confirmed

Bug description:
  I am logged in as 'nanook', I am in the tty group:
  id
  uid=2000(nanook) gid=1000(shell) groups=1000(shell),4(adm),5(tty),24(cdrom),27(sudo),30(dip),46(plugdev),118(lpadmin),128(sambashare),135(lxd)
  Yet when I say,
  write nanook
  I get
  write: effective gid does not match group of /dev/pts/5
  ls -l /dev/pts/5
  crw--w---- 1 nanook tty 136, 5 May  2 18:51 /dev/pts/5
  So something is wrong.  And since it seems to involve permissions there may be security issues.

  ProblemType: Bug
  DistroRelease: Ubuntu 22.04
  Package: util-linux 2.37.2-4ubuntu3.4
  ProcVersionSignature: Ubuntu 5.15.0-102.112-generic 5.15.148
  Uname: Linux 5.15.0-102-generic x86_64
  ApportVersion: 2.20.11-0ubuntu82.5
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: MATE
  Date: Thu May  2 18:47:55 2024
  SourcePackage: util-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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