Re: Program crashes on stable/13 (but not on 12.3)

On Sun, Mar 06, 2022 at 04:26:10AM +0700, Eugene Grosbein wrote:
! 06.03.2022 2:26, Peter wrote:
! 
! Adding kib@ to CC: in case this is connected to recent commit by him.

It is.
 
! > Hija,
! > 
! >  this program crashes SEGV on stable/13 after 135962 iterations,
! > but continues to run on 12.3.
! > 
! > My stable/13 is still at 22ba2970766 - if You happen to be on a
! > newer level, then please just try this out.
! > 
! > ------------------------------------------------------
! > #include <unistd.h>
! > #include <fcntl.h>
! > #include <stdio.h>
! > 
! > main() {
! >     char buf[] = "12345678901234567890123456789012345678901234567890";
! >     int fd = open("/dev/null", O_RDONLY);
! >     int i = 0;
! > 
! >     close(1);
! >     dup2(fd, 1);
! >     close(fd);
! > 
! >     while(1) {
! >       fputs(buf, stdout);
! >       fflush(stdout);
! >       i++;
! >       fprintf(stderr, "%d\n", i);
! >     }
! > }
! > ------------------------------------------------------
! > 
! > I know that the code is bogus, but this is exactly what one of our
! > ports does (and why it started to crash after upgrading to stable/13).
! > 
! > And I think it should not SEGV, anyway.
! > 
! > For the full story, read here:
! > 
! > https://forums.freebsd.org/threads/random-program-crashes-no-coredumps-and-error-94.84285/
! 
! fflush() in our libc recently got some change due to very old PR
! https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=76398
! 
! That change was merged to stable/13 after 13.0-RELEASE:
! https://cgit.freebsd.org/src/commit/?id=afa9a1f5ec9974793a8744c55036ef5c4d08903d

Yes, this is the cause, I now checked before and after. I don't really
see why it does what it does, even less why it only happens after so
many invocations.

I wouldn't bother much about it, because such crappy code somehow
deserves to crash - but then, concerned is sysutils/bareos-client
backup tool, and arbitrary memory corruption appears there, and I
am not sure if this could lead to silently corrupted backup data.
So it's probably not the best idea to keep this into 13.1.