abuild-sudo: fix segfault when there are no controlling term

if there are no controlling reminal getlogin() may return NULL. We use
getpwuid() to try figure out the username and verify that we actually
have a username before we set environment USER.

abuild-sudo.c

@@ -12,6 +12,7 @@
 
 #include <err.h>
 #include <grp.h>
+#include <pwd.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -70,17 +71,28 @@ int main(int argc, const char *argv[])
 	const char *cmd;
 	const char *path;
 	int i;
+	struct passwd *pw;
 
 	grent = getgrnam(ABUILD_GROUP);
 	if (grent == NULL)
 		errx(1, "%s: Group not found", ABUILD_GROUP);
 
 	char *name = getlogin();
+	if (name == NULL) {
+		pw = getpwuid(getuid());
+		if (pw)
+			name = pw->pw_name;
+	}
+
 	if (!is_in_group(grent->gr_gid)) {
 		errx(1, "User %s is not a member of group %s\n",
 			name ? name : "(unknown)", ABUILD_GROUP);
 	}
-	setenv("USER", name, 1);
+	if (name) {
+		setenv("USER", name, 1);
+	} else {
+		warnx("Could not find username for uid %d\n", getuid());
+	}
 
 	cmd = strrchr(argv[0], '/');
 	if (cmd)