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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 14 Jul 2014 08:45:29 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r268608 - head/sys/fs/tmpfs
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Author: kib
Date: Mon Jul 14 08:45:29 2014
New Revision: 268608
URL: http://svnweb.freebsd.org/changeset/base/268608

Log:
  The tmpfs_link() must not dereference the filesystem-specific data for
  a vnode until it is verified that the vnode indeed belongs to tmpfs
  mount.  Otherwise, it might access random memory, at least in the
  debug kernel.
  
  Reported and tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks

Modified:
  head/sys/fs/tmpfs/tmpfs_vnops.c

Modified: head/sys/fs/tmpfs/tmpfs_vnops.c
==============================================================================
--- head/sys/fs/tmpfs/tmpfs_vnops.c	Mon Jul 14 08:41:13 2014	(r268607)
+++ head/sys/fs/tmpfs/tmpfs_vnops.c	Mon Jul 14 08:45:29 2014	(r268608)
@@ -570,8 +570,6 @@ tmpfs_link(struct vop_link_args *v)
 	MPASS(cnp->cn_flags & HASBUF);
 	MPASS(dvp != vp); /* XXX When can this be false? */
 
-	node = VP_TO_TMPFS_NODE(vp);
-
 	/* XXX: Why aren't the following two tests done by the caller? */
 
 	/* Hard links of directories are forbidden. */
@@ -586,6 +584,8 @@ tmpfs_link(struct vop_link_args *v)
 		goto out;
 	}
 
+	node = VP_TO_TMPFS_NODE(vp);
+
 	/* Ensure that we do not overflow the maximum number of links imposed
 	 * by the system. */
 	MPASS(node->tn_links <= LINK_MAX);