Package: libc6-dev
Version: 2.28-10
Severity: normal
When running following code:
```C
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
close( STDIN_FILENO );
close( STDOUT_FILENO );
int fd = dup( STDERR_FILENO );
close( STDERR_FILENO );
if( -1 == fprintf( stdout, "%d\n", fd ) )
{
return -1;
}
char s[] = "should fail\n";
if( -1 == write( STDOUT_FILENO, s, sizeof( s ) ) )
{
return -2;
}
return EXIT_SUCCESS;
}
```
built with glibc, the program returns 254. When built with muslc, it
returns the expected value of 255.
I believe glibc's behavior here is wrong. From what I could get by using
strace, it seems that the 1st printf's write() call is ran _after_ the
2nd one, even when adding a call to fflush( stdout ) right after the
printf.
A way to make the code behaving as one would expect is to add a fprintf
call before closing descriptor. It then behaves as expected with both
libCs.
-- System Information:
Debian Release: 10.7
APT prefers stable
APT policy: (990, 'stable'), (500, 'stable-updates')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 4.19.0-13-amd64 (SMP w/4 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8),
LANGUAGE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: runit (via /run/runit.stopit)
Versions of packages libc6-dev depends on:
ii libc-dev-bin 2.28-10
ii libc6 2.28-10
ii linux-libc-dev 4.19.160-2
libc6-dev recommends no packages.
Versions of packages libc6-dev suggests:
pn glibc-doc <none>
ii manpages-dev 4.16-2
-- no debconf information
