Make pw_scan(3) more compatible with getpwent(3) et. al. when processing

data from /etc/passwd rather than /etc/master.passwd.

The libc getpwent(3) and related functions automatically read master.passwd
when run by root, or passwd when run by a non-root user.  When run by non-
root, getpwent() copes with the missing data by setting the corresponding
fields in the passwd struct to known values (zeroes for numbers, or a
pointer to an empty string for literals).  When libutil's pw_scan(3) was
used to parse a line without the root-accessible data, it was leaving
garbage in the corresponding fields.

These changes rename the static pw_init() function used by getpwent() and
friends to __pw_initpwd(), and move it into pw_scan.c so that common init
code can be shared between libc and libutil.  pw_scan(3) now calls
__pw_initpwd() before __pw_scan(), just like the getpwent() family does, so
that reading an arbitrary passwd file in either format and parsing it with
pw_scan(3) returns the same results as getpwent(3) would.

This also adds a new pw_initpwd(3) function to libutil, so that code which
creates passwd structs from scratch in some manner that doesn't involve
pw_scan() can initialize the struct to the values expected by lots of
existing code, which doesn't expect to encounter NULL pointers or garbage
values in some fields.

2 files changed, 17 insertions, 0 deletions

diff --git a/libc/gen/pw_scan.c b/libc/gen/pw_scan.c
index a7dbdf2..619092d 100644
--- a/libc/gen/pw_scan.c
+++ b/libc/gen/pw_scan.c
@@ -65,6 +65,22 @@ __FBSDID("$FreeBSD$");
  */
 static int	pw_big_ids_warning = 0;
 
+void
+__pw_initpwd(struct passwd *pwd)
+{
+	static char nul[] = "";
+
+	memset(pwd, 0, sizeof(*pwd));
+	pwd->pw_uid = (uid_t)-1;  /* Considered least likely to lead to */
+	pwd->pw_gid = (gid_t)-1;  /* a security issue.                  */
+	pwd->pw_name = nul;
+	pwd->pw_passwd = nul;
+	pwd->pw_class = nul;
+	pwd->pw_gecos = nul;
+	pwd->pw_dir = nul;
+	pwd->pw_shell = nul;
+}
+
 int
 __pw_scan(char *bp, struct passwd *pw, int flags)
 {
diff --git a/libc/gen/pw_scan.h b/libc/gen/pw_scan.h
index 44ff818..b567036 100644
--- a/libc/gen/pw_scan.h
+++ b/libc/gen/pw_scan.h
@@ -35,4 +35,5 @@
 #define _PWSCAN_MASTER 0x01
 #define _PWSCAN_WARN   0x02
 
+extern void	__pw_initpwd(struct passwd *);
 extern int	__pw_scan(char *, struct passwd *, int);