errno should be reset to 0 before each call to getpwent() in genhomedircon

[bigon]

Hello,

In genhomedircon, it seems that errno should be reset to 0 before each call to getpwent()

The manpage of getpwent() states:

The getpwent() function returns a pointer to a passwd structure, or NULL if there are no more entries or an error occurred. If an error occurs, errno is set appropriately. If one wants to check errno after the call, it should be set to zero before the call.

Without this, genhomedircon can wrongly return the following error when using the files module:

libsemanage.get_home_dirs: Error while fetching users. Returning list so far.

[fishilico]

The catch is this issue is that getpwent can set errno = EINVAL when returning entries, which is why errno needs to be set to 0 every time getpwent is called.

For future reference, here is a simple test program to illustrate this behavior:

#include <sys/types.h>
#include <pwd.h>
#include <errno.h>
#include <stdio.h>

int main(void)
{
    struct passwd *pw;
    setpwent();
    errno = 0;
    while ((pw = getpwent()) != NULL) {
        printf("%d: %s (errno %d)\n", pw->pw_uid, pw->pw_name, errno);
	errno = 0;
    }
    printf("getpwent errno = %d (%m)\n", errno);
    endpwent();
    return 0;
}

Its output (in a Vagrant virtual machine with glibc 2.28 and systemd 239.370 is:

0: root (errno 22)
1: bin (errno 22)
2: daemon (errno 22)
8: mail (errno 22)
14: ftp (errno 22)
33: http (errno 22)
68: uuidd (errno 22)
81: dbus (errno 22)
99: nobody (errno 22)
191: systemd-journal-gateway (errno 22)
192: systemd-timesync (errno 22)
193: systemd-network (errno 22)
194: systemd-bus-proxy (errno 22)
195: systemd-resolve (errno 22)
998: systemd-journal-remote (errno 22)
999: systemd-coredump (errno 22)
997: systemd-journal-upload (errno 22)
1000: vagrant (errno 22)
994: git (errno 22)
993: avahi (errno 22)
992: colord (errno 22)
102: polkitd (errno 22)
getpwent errno = 0 (Success)

I merged your commit. Thanks!