fix the “set ±p” issue for good

cf. http://blog.cmpxchg8b.com/2013/08/security-debianisms.html

main.c

@@ -34,7 +34,7 @@
 #include <locale.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/main.c,v 1.279 2014/01/16 13:59:12 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/main.c,v 1.280 2014/06/09 12:28:17 tg Exp $");
 
 extern char **environ;
 
@@ -407,7 +407,7 @@ main_init(int argc, const char *argv[], Source **sp, struct block **lp)
 	setint_n((vp_pipest = global("PIPESTATUS")), 0, 10);
 
 	/* Set this before parsing arguments */
-	Flag(FPRIVILEGED) = kshuid != ksheuid || kshgid != kshegid;
+	Flag(FPRIVILEGED) = (kshuid != ksheuid || kshgid != kshegid) ? 2 : 0;
 
 	/* this to note if monitor is set on command line (see below) */
 #ifndef MKSH_UNEMPLOYED
@@ -585,22 +585,22 @@ main_init(int argc, const char *argv[], Source **sp, struct block **lp)
 	if (!current_wd[0] && Flag(FTALKING))
 		warningf(false, "can't determine current directory");
 
-	if (Flag(FLOGIN)) {
+	if (Flag(FLOGIN))
 		include(MKSH_SYSTEM_PROFILE, 0, NULL, true);
-		if (!Flag(FPRIVILEGED))
-			include(substitute("$HOME/.profile", 0), 0,
-			    NULL, true);
-	}
-	if (Flag(FPRIVILEGED))
+	if (!Flag(FPRIVILEGED)) {
+		if (Flag(FLOGIN))
+			include(substitute("$HOME/.profile", 0), 0, NULL, true);
+		if (Flag(FTALKING)) {
+			cp = substitute(substitute("${ENV:-" MKSHRC_PATH "}",
+			    0), DOTILDE);
+			if (cp[0] != '\0')
+				include(cp, 0, NULL, true);
+		}
+	} else {
 		include(MKSH_SUID_PROFILE, 0, NULL, true);
-	else if (Flag(FTALKING)) {
-		char *env_file;
-
-		/* include $ENV */
-		env_file = substitute(substitute("${ENV:-" MKSHRC_PATH "}", 0),
-		    DOTILDE);
-		if (*env_file != '\0')
-			include(env_file, 0, NULL, true);
+		/* turn off -p if not set explicitly */
+		if (Flag(FPRIVILEGED) != 1)
+			change_flag(FPRIVILEGED, OF_INTERNAL, false);
 	}
 
 	if (restricted) {

mksh.1

@@ -1,4 +1,4 @@
-.\" $MirOS: src/bin/mksh/mksh.1,v 1.334 2014/06/09 11:22:50 tg Exp $
+.\" $MirOS: src/bin/mksh/mksh.1,v 1.335 2014/06/09 12:28:17 tg Exp $
 .\" $OpenBSD: ksh.1,v 1.152 2014/02/12 16:28:13 schwarze Exp $
 .\"-
 .\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
@@ -247,8 +247,7 @@ below.
 Privileged shell.
 A shell is
 .Dq privileged
-if this option is used
-or if the real user ID or group ID does not match the
+if the real user ID or group ID does not match the
 effective user ID or group ID (see
 .Xr getuid 2
 and
@@ -257,6 +256,9 @@ Clearing the privileged option causes the shell to set
 its effective user ID (group ID) to its real user ID (group ID).
 For further implications, see
 .Sx Startup files .
+If the shell is privileged and this flag is not explicitly set, the
+.Dq privileged
+option is cleared automatically after processing the startup files.
 .It Fl r
 Restricted shell.
 A shell is
@@ -366,15 +368,9 @@ parameter after subjecting it to parameter, command, arithmetic and tilde
 substitution; if unset or empty, the user mkshrc profile is processed;
 otherwise, if a file whose name is the substitution result exists,
 it is processed; non-existence is silently ignored.
-.Pp
-The suid profile probably should run
-.Ic set +p
-unless the shell was explicitly started with
-.Fl p .
-This isn't easily implemented but
-.Pq just always run Ic set +p
-a stopgap measure for:
-.Pa http://blog.cmpxchg8b.com/2013/08/security\-debianisms.html
+A privileged shell then drops privileges if neither was the
+.Fl p
+option given on the command line nor set during execution of the startup files.
 .Ss Command syntax
 The shell begins parsing its input by removing any backslash-newline
 combinations, then breaking it into
@@ -6457,7 +6453,7 @@ $ /bin/sleep 666 && echo fubar
 .Ed
 .Pp
 This document attempts to describe
-.Nm mksh\ R49
+.Nm mksh\ R50
 and up,
 compiled without any options impacting functionality, such as
 .Dv MKSH_SMALL ,

sh_flags.opt

@@ -1,5 +1,5 @@
 @SHFLAGS_DEFNS
-__RCSID("$MirOS: src/bin/mksh/sh_flags.opt,v 1.1 2013/11/17 22:22:56 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/sh_flags.opt,v 1.2 2014/06/09 12:28:19 tg Exp $");
 #define FN(sname,cname,flags,ochar)		\
 	static const struct {			\
 		/* character flag (if any) */	\
@@ -123,7 +123,7 @@ FN("pipefail", FPIPEFAIL, OF_ANY
 >|
 FN("posix", FPOSIX, OF_ANY
 
-/* -p	use suid_profile; privileged shell */
+/* -p	privileged shell (suid) */
 >p|
 FN("privileged", FPRIVILEGED, OF_ANY