[Bug 2067916] Re: libc6: broken utmp handling in 32-bit programs with 64-bit time_t

[Bug Watch Updater]

** Changed in: glibc (Debian)
       Status: New => Fix Released

** Changed in: glibc (Debian)
   Importance: Undecided => Unknown

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Title:
  libc6: broken utmp handling in 32-bit programs with 64-bit time_t

Status in glibc package in Ubuntu:
  New
Status in glibc source package in Noble:
  New
Status in glibc source package in Oracular:
  New
Status in glibc package in Debian:
  Fix Released

Bug description:
  Imported from Debian bug http://bugs.debian.org/1042562:

  Package: libc6
  Version: 2.37-6
  Tags: upstream

  The utmp(5) interface has broken its compatibility in 32-bit programs
  built with -D_TIME_BITS=64.  In bits/utmpx.h we see this:

  ,----
  | /* The fields ut_session and ut_tv must be the same size when compiled
  |    32- and 64-bit.  This allows files and shared memory to be shared
  |    between 32- and 64-bit applications.  */
  | #if __WORDSIZE_TIME64_COMPAT32
  |   __int32_t ut_session;		/* Session ID, used for windowing.  */
  |   struct
  |   {
  |     __int32_t tv_sec;		/* Seconds.  */
  |     __int32_t tv_usec;		/* Microseconds.  */
  |   } ut_tv;			/* Time entry was made.  */
  | #else
  |   long int ut_session;		/* Session ID, used for windowing.  */
  |   struct timeval ut_tv;		/* Time entry was made.  */
  | #endif
  `----

  The definition of __WORDSIZE_TIME64_COMPAT32 can be found in
  bits/wordsize.h:

  ,----
  | #ifdef __x86_64__
  | # define __WORDSIZE_TIME64_COMPAT32	1
  | /* Both x86-64 and x32 use the 64-bit system call interface.  */
  | # define __SYSCALL_WORDSIZE		64
  | #else
  | # define __WORDSIZE_TIME64_COMPAT32	0
  | #endif
  `----

  So on i386 (and I suppose on other 32-bit architectures except x32)
  ut_tv is of struct timeval, and ut_tv.tv_sec is of time_t, which is
  actually a 64-bit integer in programs built with -D_TIME_BITS=64.

  One example where this already has caused problems is the who(1) program
  which has opted in for -D_TIME_BITS=64, see #1027135.  Once programs
  start to _write_ utmp entries with a 64-bit ut_tv.tv_sec rather than
  merely reading them, things could become more interesting. :-(

  
  -- System Information:
  Debian Release: trixie/sid
    APT prefers unstable
    APT policy: (500, 'unstable'), (101, 'experimental')
  Architecture: amd64 (x86_64)
  Foreign Architectures: i386

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