svn commit: r348538 - stable/12/lib/libjail

[Kyle Evans]

Author: kevans
Date: Mon Jun  3 15:28:37 2019
New Revision: 348538
URL: https://svnweb.freebsd.org/changeset/base/348538

Log:
  MFC r348509: jail_getid(3): add special-case immediate return for jid 0
  
  As depicted in the comment: jid 0 always exists, but the lookup will fail as
  it does not appear in the kernel's alljails list being a special jail. Some
  callers will expect/rely on this, and we have no reason to lie because it
  does always exist.
  
  Approved by:	re (early MFC)

Modified:
  stable/12/lib/libjail/jail_getid.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/lib/libjail/jail_getid.c
==============================================================================
--- stable/12/lib/libjail/jail_getid.c	Mon Jun  3 15:25:12 2019	(r348537)
+++ stable/12/lib/libjail/jail_getid.c	Mon Jun  3 15:28:37 2019	(r348538)
@@ -54,6 +54,15 @@ jail_getid(const char *name)
 
 	jid = strtoul(name, &ep, 10);
 	if (*name && !*ep) {
+		/*
+		 * jid == 0 is a special case; it will not appear in the
+		 * kernel's jail list, but naturally processes will be assigned
+		 * to it because it is prison 0.  Trivially return this one
+		 * without a trip to the kernel, because it always exists but
+		 * the lookup won't succeed.
+		 */
+		if (jid == 0)
+			return jid;
 		jiov[0].iov_base = __DECONST(char *, "jid");
 		jiov[0].iov_len = sizeof("jid");
 		jiov[1].iov_base = &jid;