[129/262] VFS: Fix automount for negative autofs dentries

[Greg KH]

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@xxxxxxxxxx>

commit 5a30d8a2b8ddd5102c440c7e5a7c8e1fd729c818 upstream.
[ backport for 3.0.x: LOOKUP_PARENT => LOOKUP_CONTINUE by Chuck Ebbert
<cebbert@xxxxxxxxxx> ]

Autofs may set the DCACHE_NEED_AUTOMOUNT flag on negative dentries.  These
need attention from the automounter daemon regardless of the LOOKUP_FOLLOW flag.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Acked-by: Ian Kent <raven@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/namei.c |   24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -781,19 +781,25 @@ static int follow_automount(struct path
 	if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
 		return -EISDIR; /* we actually want to stop here */
 
-	/* We want to mount if someone is trying to open/create a file of any
-	 * type under the mountpoint, wants to traverse through the mountpoint
-	 * or wants to open the mounted directory.
-	 *
+	/*
 	 * We don't want to mount if someone's just doing a stat and they've
 	 * set AT_SYMLINK_NOFOLLOW - unless they're stat'ing a directory and
 	 * appended a '/' to the name.
 	 */
-	if (!(flags & LOOKUP_FOLLOW) &&
-	    !(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY |
-		       LOOKUP_OPEN | LOOKUP_CREATE)))
-		return -EISDIR;
-
+	if (!(flags & LOOKUP_FOLLOW)) {
+		/* We do, however, want to mount if someone wants to open or
+		 * create a file of any type under the mountpoint, wants to
+		 * traverse through the mountpoint or wants to open the mounted
+		 * directory.
+		 * Also, autofs may mark negative dentries as being automount
+		 * points.  These will need the attentions of the daemon to
+		 * instantiate them before they can be used.
+		 */
+		if (!(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY |
+			     LOOKUP_OPEN | LOOKUP_CREATE)) &&
+		    path->dentry->d_inode)
+			return -EISDIR;
+	}
 	current->total_link_count++;
 	if (current->total_link_count >= 40)
 		return -ELOOP;


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