pgagroal-admin segfault when -f file is missing

[will]

Describe the bug

Segfault when the file passed in in -f is not present.

To Reproduce

[centos ~]$ sudo -u pgagroal ls /home/pgagroal/.pgagroal
master.key
[centos ~]$ ls /etc/pgagroal/
pgagroal.conf  pgagroal_hba.conf

[centos ~]$ sudo -u pgagroal pgagroal-admin -f /etc/pgagroal/pgagroal_users.conf add-user -U postgres
Segmentation fault

Debug logs

[centos ~]$ sudo coredumpctl gdb 3448386
           PID: 3448386 (pgagroal-admin)
           UID: 990 (pgagroal)
           GID: 987 (pgagroal)
        Signal: 11 (SEGV)
     Timestamp: Tue 2021-03-16 19:02:01 UTC (40s ago)
  Command Line: pgagroal-admin -f /etc/pgagroal/pgagroal_users.conf add-user -U postgres
    Executable: /usr/bin/pgagroal-admin
 Control Group: /user.slice/user-1000.slice/session-373.scope
          Unit: session-373.scope
         Slice: user-1000.slice
       Session: 373
     Owner UID: 1000 (centos)
       Storage: /var/lib/systemd/coredump/core.pgagroal-admin.990.72d624ef3e1845de9ef0e8e920094516.3448386.1615921321000000.lz4
       Message: Process 3448386 (pgagroal-admin) of user 990 dumped core.

                Stack trace of thread 3448386:
                #0  0x00007f5a19ec72ef _IO_fgets (libc.so.6)
                #1  0x000055ad9cbf7bf9 add_user (pgagroal-admin)
                #2  0x000055ad9cbf7396 main (pgagroal-admin)
                #3  0x00007f5a19e797b3 __libc_start_main (libc.so.6)
                #4  0x000055ad9cbf750e _start (pgagroal-admin)


(gdb) bt
#0  0x00007f5a19ec72ef in fgets () from /usr/lib64/libc.so.6
#1  0x000055ad9cbf7bf9 in add_user (users_path=<optimized out>, username=0x7fffbdd3177c "postgres", password=0x0, generate_pwd=<optimized out>, pwd_length=64)
    at /usr/src/debug/pgagroal-1.2.0-1Crunchy.el8.x86_64/src/admin.c:476
#2  0x000055ad9cbf7396 in main (argc=<optimized out>, argv=0x7fffbdd30c98) at /usr/src/debug/pgagroal-1.2.0-1Crunchy.el8.x86_64/src/admin.c:208
(gdb) list
94	   printf("\n");
95	   printf("Commands:\n");
96	   printf("  master-key              Create or update the master key\n");
97	   printf("  add-user                Add a user\n");
98	   printf("  update-user             Update a user\n");
99	   printf("  remove-user             Remove a user\n");
100	   printf("  list-users              List all users\n");
101	   printf("\n");
102	   printf("pgagroal: %s\n", PGAGROAL_HOMEPAGE);
103	   printf("Report bugs: %s\n", PGAGROAL_ISSUES);

(gdb) f 1
#1  0x000055ad9cbf7bf9 in add_user (users_path=<optimized out>, username=0x7fffbdd3177c "postgres", password=0x0, generate_pwd=<optimized out>, pwd_length=64)
    at /usr/src/debug/pgagroal-1.2.0-1Crunchy.el8.x86_64/src/admin.c:476
476	   while (fgets(line, sizeof(line), users_file))
(gdb) list
471	   {
472	      goto username;
473	   }
474
475	   /* Verify */
476	   while (fgets(line, sizeof(line), users_file))
477	   {
478	      ptr = strtok(line, ":");
479	      if (!strcmp(username, ptr))
480	      {

(gdb) p users_file
$2 = (FILE *) 0x0


(gdb) f 2
#2  0x000055ad9cbf7396 in main (argc=<optimized out>, argv=0x7fffbdd30c98) at /usr/src/debug/pgagroal-1.2.0-1Crunchy.el8.x86_64/src/admin.c:208
208	            if (add_user(file_path, username, password, generate_pwd, pwd_length))
(gdb) list
203	      }
204	      else if (action == ACTION_ADD_USER)
205	      {
206	         if (file_path != NULL)
207	         {
208	            if (add_user(file_path, username, password, generate_pwd, pwd_length))
209	            {
210	               printf("Error for add-user\n");
211	               exit_code = 1;
212	            }


(gdb) p file_path
$3 = 0x7fffbdd3174e "/etc/pgagroal/pgagroal_users.conf"
(gdb) p username
$4 = 0x7fffbdd3177c "postgres"
(gdb) p password
$5 = 0x0
(gdb) p generate_pwd
$6 = false
(gdb) p pwd_length
$7 = 64

[jesperpedersen]

Fixed the segfault, and output reason for file error.

Thanks Will !