Preserve (instead of collapse) arguments in su_monkeysphere_user().autoquote

It is a healthy coding practice to keep each argument separate when
executing system calls, i.e. quote each variable separately instead of
relying on whitespace to indicate argument separation.

Quoting shell-inside-shell is tricky to do right, but not impossible:

Bourne-derived shells treat single-quoting literally, which means that
shell command arguments (i.e. an array of strings) should be safe to
serialize (dual-quote) using these simple rules:

 b) each single-quote inside each string is escaped as '\''
 a) each string is surrounded by single-quotes

This patch applies above single-quote serialization for
su_monkeysphere_user(), and adapts ma/update_users $STRICT_MODES on
line 82 to match.

If serialization routine should turn out to be broken, it will
therefore only affect $STRICT_MODES in ma/update_users badly.  All other
variables passed through su_monkeysphere_user() should not possibly be
treated any worse than previous non-quoting.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/share/common b/src/share/common
index f9be05a..4dd46c8 100644
--- a/src/share/common
+++ b/src/share/common
@@ -100,15 +100,19 @@ su_monkeysphere_user() {
     # introduce an extra dependency just for this.  This may be a
     # candidate for re-factoring if we switch implementation languages.
 
+    # singlequote-escape strings - like this bashism:
+    #   printf -v CMDLINE "%q " "$@"
+    local CMDLINE="$(perl -0 -e "foreach (@ARGV) {s/'/'\\\\''/g; print \"'\$_' \"}" "$@")"
+
     case $(id -un) in
 	# if monkeysphere user, run the command under bash
 	"$MONKEYSPHERE_USER")
-	    bash -c "$*"
+	    bash -c "$CMDLINE"
 	    ;;
 
          # if root, su command as monkeysphere user
 	'root')
-	    su "$MONKEYSPHERE_USER" -c "$*"
+	    su "$MONKEYSPHERE_USER" -c "$CMDLINE"
 	    ;;
 
 	# otherwise, fail