MAC/do: Fix jail_get() (PR_METHOD_GET)

- Properly fill 'jsys' before copying it out (we would leak bytes from
  the kernel stack).  When the current jail has its own 'struct rules',
  set it to the special value JAIL_SYS_DISABLE if it in fact holds no
  rules.
- Don't forget to unlock the jail holding rules on error.
- Correctly return errors.

Reviewed by:    bapt
Approved by:    markj (mentor)
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D47609

1 files changed, 10 insertions, 4 deletions

diff --git a/sys/security/mac_do/mac_do.c b/sys/security/mac_do/mac_do.c
index 6f68a6f62a79..2482221e43a3 100644
--- a/sys/security/mac_do/mac_do.c
+++ b/sys/security/mac_do/mac_do.c
@@ -353,22 +353,28 @@ mac_do_jail_create(void *obj, void *data __unused)
 static int
 mac_do_jail_get(void *obj, void *data)
 {
-	struct prison *ppr, *pr = obj;
-	struct vfsoptlist *opts = data;
+	struct prison *ppr, *const pr = obj;
+	struct vfsoptlist *const opts = data;
 	struct rules *rules;
 	int jsys, error;
 
 	rules = find_rules(pr, &ppr);
+
+	jsys = pr == ppr ?
+	    (TAILQ_EMPTY(&rules->head) ? JAIL_SYS_DISABLE : JAIL_SYS_NEW) :
+	    JAIL_SYS_INHERIT;
 	error = vfs_setopt(opts, "mac.do", &jsys, sizeof(jsys));
 	if (error != 0 && error != ENOENT)
 		goto done;
+
 	error = vfs_setopts(opts, "mac.do.rules", rules->string);
 	if (error != 0 && error != ENOENT)
 		goto done;
-	prison_unlock(ppr);
+
 	error = 0;
 done:
-	return (0);
+	prison_unlock(ppr);
+	return (error);
 }
 
 static int