user mod -u lead to segfault

[Moritz Buhl]

Hi,

when using user mod -u, my machine ran into a segfault and the passwd
file was left locked.

I belief this is due to the changes to getpwnam etc.
Sadly I am unable to figure out, why exactly the call to getpwuid
segfaults. But replacing it with a call to user_from_uid helped.
I could not crash the program with other flags that use getpw{nam,uid}.

Thanks,
Moritz Buhl


Index: user.c
===================================================================
RCS file: /cvs/src/usr.sbin/user/user.c,v
retrieving revision 1.122
diff -u -p -r1.122 user.c
--- user.c      26 Sep 2018 14:54:58 -0000      1.122
+++ user.c      8 Oct 2018 17:00:16 -0000
@@ -1515,7 +1515,8 @@ moduser(char *login_name, char *newlogin
                }
                if (up->u_flags & F_UID) {
                        /* check uid isn't already allocated */
-                       if (!(up->u_flags & F_DUPUID) && 
getpwuid((uid_t)(up->u_uid)) != NULL) {
+                       if (!(up->u_flags & F_DUPUID) &&
+                           user_from_uid((uid_t)(up->u_uid), 1) != NULL) {
                                close(ptmpfd);
                                pw_abort();
                                errx(EXIT_FAILURE, "uid %u is already in use", 
up->u_uid);