Fix using more than one files in UID_FILES and GID_FILES.

Repeat after me: If you change IFS, it will break something unexpected.

The problem is that we use IFS to change read's field separator.  This
has the side effect of changing how sh(1) splits all string, including
in command parsing functions.

In this case, unless quoted, the strings are always splitted using IFS.
So changing IFS will change how these strings are splitted, and you end
up having a headache.  For example:

    $ GID_FILES="foo bar"
    $ set -x
    $ echo $GID_FILES
    + echo foo bar
    foo bar

    $ IFS=:
    $ GID_FILES="foo bar"
    $ set -x
    $ echo $GID_FILES
    + echo 'foo bar'
    foo bar

In the first case, it runs echo with two arguments, first is foo, second is bar.
In the second case, it runs echo with one argument, 'foo bar'.

To fix this, restrict the time during which IFS changes to only one
command, set, and use positional parameters to extract values.

Reported by:	feld
Sponsored by:	Absolight
Differential Revision:	https://reviews.freebsd.org/D11632

Mk/Scripts/do-users-groups.sh

@@ -25,6 +25,10 @@ error() {
 	exit 1
 }
 
+# Lines from GID and UID files both contain *. As we do not need any pathname
+# expansion, disable globbing.
+set -f
+
 rm -f "${dp_UG_INSTALL}" "${dp_UG_DEINSTALL}" || :
 
 # Before FreeBSD 10.2, PW did not have -R support.
@@ -56,9 +60,16 @@ if [ -n "${GROUPS}" ]; then
 		if ! grep -q "^${group}:" ${dp_GID_FILES}; then \
 			error "** Cannot find any information about group \`${group}' in ${dp_GID_FILES}."
 		fi
-		o_IFS=${IFS}
-		IFS=":"
-		while read -r group _ gid _; do
+		while read -r line; do
+			# Do not change IFS for more than one command, if we
+			# changed IFS around the while read, it would mess up
+			# the string splitting in the heredoc command.
+			o_IFS=${IFS}
+			IFS=":"
+			set -- ${line}
+			IFS=${o_IFS}
+			group=$1
+			gid=$3
 			if [ -z "${gid}" ]; then
 				error "Group line for group ${group} has no gid"
 			fi
@@ -74,7 +85,6 @@ if [ -n "${GROUPS}" ]; then
 		done <<-eot
 		$(grep -h "^${group}:" ${dp_GID_FILES} | head -n 1)
 		eot
-		IFS=${o_IFS}
 	done
 fi
 
@@ -93,9 +103,21 @@ if [ -n "${USERS}" ]; then
 		if ! grep -q "^${user}:" ${dp_UID_FILES} ; then
 			error "** Cannot find any information about user \`${user}' in ${dp_UID_FILES}."
 		fi
-		o_IFS=${IFS}
-		IFS=":"
-		while read -r login _ uid gid class _ _ gecos homedir shell; do
+		while read -r line; do
+			# Do not change IFS for more than one command, if we
+			# changed IFS around the while read, it would mess up
+			# the string splitting in the heredoc command.
+			o_IFS=${IFS}
+			IFS=":"
+			set -- ${line}
+			IFS=${o_IFS}
+			login=$1
+			uid=$3
+			gid=$4
+			class=$5
+			gecos=$8
+			homedir=$9
+			shell=${10}
 			if [ -z "$uid" ] || [ -z "$gid" ] || [ -z "$homedir" ] || [ -z "$shell" ]; then
 				error "User line for ${user} is invalid"
 			fi
@@ -124,20 +146,31 @@ if [ -n "${USERS}" ]; then
 		done <<-eot
 		$(grep -h "^${user}:" ${dp_UID_FILES} | head -n 1)
 		eot
-		IFS=${o_IFS}
 	done
 fi
 
 if [ -n "${GROUPS}" ]; then
 	for group in ${GROUPS}; do
 		# mail:*:6:postfix,clamav
-		o_IFS=${IFS}
-		IFS=":"
-		while read -r group _ gid members; do
+		while read -r line; do
+			# Do not change IFS for more than one command, if we
+			# changed IFS around the while read, it would mess up
+			# the string splitting in the heredoc command.
+			o_IFS=${IFS}
+			IFS=":"
+			# As some lines do not have a fourth argument, provide
+			# one so $4 always exists.
+			set -- ${line} ""
+			IFS=${o_IFS}
+			group=$1
+			gid=$3
+			members=$4
 			gid=$((gid+dp_GID_OFFSET))
-			oo_IFS=${IFS}
+			o_IFS=${IFS}
 			IFS=","
-			for login in $members; do
+			set -- ${members}
+			IFS=${o_IFS}
+			for login in "$@"; do
 				for user in ${USERS}; do
 					if [ -n "${user}" ] && [ "${user}" = "${login}" ]; then
 						cat >> "${dp_UG_INSTALL}" <<-eot2
@@ -149,11 +182,9 @@ if [ -n "${GROUPS}" ]; then
 					fi
 				done
 			done
-			IFS=${oo_IFS}
 		done <<-eot
 		$(grep -h "^${group}:" ${dp_GID_FILES} | head -n 1)
 		eot
-		IFS=${o_IFS}
 	done
 fi