Implement PF_IMMUTABLE flag and apply it to "name" and "jid" in

jail.conf parameters.  This flag disallows redefinition of the parameter.

"name" and/or "jid" are automatically defined in jail.conf by using
the jail names at the front of jail parameter definitions.  However,
one could override them by using a variable with the same name like
$name = "foo".  This confused the parser and could end up with SIGSEGV.

Note that this change also affects a case when all of parameters are
defined in the command line arguments, not in jail.conf.  Specifically,
"jail -c name=j1 name=j2" no longer works.  This should be harmless.

PR:		196574
Reviewed by:	jamie
Differential Revision:	https://reviews.freebsd.org/D3017

1 files changed, 7 insertions, 2 deletions

diff --git a/usr.sbin/jail/config.c b/usr.sbin/jail/config.c
index 1dd04498bcd7..87b8ef9675a6 100644
--- a/usr.sbin/jail/config.c
+++ b/usr.sbin/jail/config.c
@@ -111,8 +111,8 @@ static const struct ipspec intparams[] = {
 #ifdef INET6
     [KP_IP6_ADDR] =		{"ip6.addr",		0},
 #endif
-    [KP_JID] =			{"jid",			0},
-    [KP_NAME] =			{"name",		0},
+    [KP_JID] =			{"jid",			PF_IMMUTABLE},
+    [KP_NAME] =			{"name",		PF_IMMUTABLE},
     [KP_PATH] =			{"path",		0},
     [KP_PERSIST] =		{"persist",		0},
     [KP_SECURELEVEL] =		{"securelevel",		0},
@@ -362,6 +362,11 @@ add_param(struct cfjail *j, const struct cfparam *p, enum intparam ipnum,
 				break;
 	if (dp != NULL) {
 		/* Found it - append or replace. */
+		if (dp->flags & PF_IMMUTABLE) {
+			jail_warnx(j, "cannot redefine variable \"%s\".",
+			    dp->name);
+			return;
+		}
 		if (strcmp(dp->name, name)) {
 			free(dp->name);
 			dp->name = estrdup(name);