Re: FreeRADIUS instability

["Pawel S. Veselov" <pawel.veselov%gmail.com@localhost>]

On 9/29/21 14:21, Pawel S. Veselov wrote:
> > As you saw the libc address lookup routines leave the fd open, and if
> > something as part of a "make sure all fd's > 2 are closed at startup"
> > type functionality went and closed it, that would cause a problem.
> > The kqueue fd is used to monitor /etc/resolv.conf for any changes that
> > would require (or might require) it to be re-read (which is a useful
> > thing to do for long running daemons) - so it needs to remain open
> > for the life of the process.
> I think my other email provides a reasonable explanation of what
> is going on. It seems to me that the sequence of getaddrinfo() -
> fork() - getaddrinfo() will always cause issues since kqueue FD is not
> inherited after fork(), but the libc address lookup routines keep the
> descriptor around.

I've put together a quick test, it behaves a bit different, but shows
the problem all the same. I expected resolv to close the fd in the same
fashion, but it doesn't IMHO because kevent() fails. The situation is
then only fatal when the child opened kqueue, and not any other socket.

ktrace shows:

(parent opens resolv kqueue)
 22888      1 gf       CALL  kqueue1(0x400000)
 22888      1 gf       RET   kqueue1 3
(fork)
 22888      1 gf       CALL  fork
 22888      1 gf       RET   fork 16605/0x40dd
(child opens an FD)
 16605      1 gf       CALL  open(0x400db2,0,0)
 16605      1 gf       NAMI  "/etc/hosts"
 16605      1 gf       RET   open 3
(resolv in child tries to use FD 3)
 16605      1 gf       CALL 
__kevent50(3,0,0,0x7f7fff7d5620,1,0x7cb75cd787b0)
 16605      1 gf       RET   __kevent50 -1 errno 9 Bad file descriptor



[root@almaz ~]$ cat gf.c
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#include <fcntl.h>

int main(int argc, char ** argv) {

        struct addrinfo * res;

        getaddrinfo("www.netbsd.org", NULL, NULL, &res);

        pid_t pid = fork();
        if (pid < 0) {
                perror("fork");
                return 1;
        }

        if (!pid) {
                // child
                int fd = open("/etc/hosts", O_RDONLY);
                getaddrinfo("www.netbsd.com", NULL, NULL, &res);
                char buf[101];
                int rc;
                while (1) {
                        rc = read(fd, buf, 100);
                        if (rc < 0) { perror("read"); }
                        if (rc <= 0) { break; }
                        buf[rc] = 0;
                        fprintf(stdout, "%s", buf);
                }
                fprintf(stdout, "\n");
                return !rc ? 0 : 1;
        } else {
                int s;
                while (1) {
                        waitpid(pid, &s, 0);
                        if (!WIFEXITED(s)) {
                                fprintf(stdout, "not ready\n");
                                continue;
                        }
                        return WEXITSTATUS(s);
                        break;
                }
        }

}