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Date:      Sun, 2 Jun 2019 14:03:57 +0000 (UTC)
From:      Kyle Evans <kevans@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r348509 - head/lib/libjail
Message-ID:  <201906021403.x52E3v0x067698@repo.freebsd.org>

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Author: kevans
Date: Sun Jun  2 14:03:56 2019
New Revision: 348509
URL: https://svnweb.freebsd.org/changeset/base/348509

Log:
  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.
  
  Reported by:	Stefan Hegnauer <stefan.hegnauer gmx ch>
  MFC after:	soon (regression, breaks inspecting jail host bits, partial
  revert)

Modified:
  head/lib/libjail/jail_getid.c

Modified: head/lib/libjail/jail_getid.c
==============================================================================
--- head/lib/libjail/jail_getid.c	Sun Jun  2 09:28:50 2019	(r348508)
+++ head/lib/libjail/jail_getid.c	Sun Jun  2 14:03:56 2019	(r348509)
@@ -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;



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