[Bug 1960210] [NEW] memstream does not add '\0' to buffer using fseek and fflush

[Jan Strater-Büddefeld]

Public bug reported:

The man page OPEN_MEMSTREAM(3) says, the buffer and size are updated
each time fflush and fclose are called and that a null byte is
maintained at the end of the buffer. The attached c program shows an
unexpected difference between fflush and fclose if you write to a
memstream and seek to the begin of the stream using fseek. Fflush
doesn't add a new null byte but fclose does.

ProblemType: Bug
DistroRelease: Ubuntu 21.10
Package: libc6 2.34-0ubuntu3
ProcVersionSignature: Ubuntu 5.13.0-28.31-generic 5.13.19
Uname: Linux 5.13.0-28-generic x86_64
ApportVersion: 2.20.11-0ubuntu71
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Mon Feb  7 10:47:19 2022
InstallationDate: Installed on 2021-03-27 (316 days ago)
InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: glibc
UpgradeStatus: Upgraded to impish on 2021-10-18 (111 days ago)

** Affects: glibc (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug impish

** Attachment added: "The bug can be reproduced using this program"
   https://bugs.launchpad.net/bugs/1960210/+attachment/5559520/+files/openMemstreamBug.c

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https://bugs.launchpad.net/bugs/1960210

Title:
  memstream does not add '\0' to buffer using fseek and fflush

Status in glibc package in Ubuntu:
  New

Bug description:
  The man page OPEN_MEMSTREAM(3) says, the buffer and size are updated
  each time fflush and fclose are called and that a null byte is
  maintained at the end of the buffer. The attached c program shows an
  unexpected difference between fflush and fclose if you write to a
  memstream and seek to the begin of the stream using fseek. Fflush
  doesn't add a new null byte but fclose does.

  ProblemType: Bug
  DistroRelease: Ubuntu 21.10
  Package: libc6 2.34-0ubuntu3
  ProcVersionSignature: Ubuntu 5.13.0-28.31-generic 5.13.19
  Uname: Linux 5.13.0-28-generic x86_64
  ApportVersion: 2.20.11-0ubuntu71
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: ubuntu:GNOME
  Date: Mon Feb  7 10:47:19 2022
  InstallationDate: Installed on 2021-03-27 (316 days ago)
  InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=de_DE.UTF-8
   SHELL=/bin/bash
  SourcePackage: glibc
  UpgradeStatus: Upgraded to impish on 2021-10-18 (111 days ago)

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