Bug#1042562: libc6: broken utmp handling in 32-bit programs with 64-bit time_t
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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