linux-kernel - [48/90] fsnotify: dont BUG in fsnotify_destroy

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Message-Id: <20120123234027.027140487@clark.kroah.org>
Date:	Mon, 23 Jan 2012 15:39:34 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Miklos Szeredi <mszeredi@...e.cz>
Subject: [48/90] fsnotify: dont BUG in fsnotify_destroy_mark()

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

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

From: Miklos Szeredi <mszeredi@...e.cz>

commit fed474857efbed79cd390d0aee224231ca718f63 upstream.

Removing the parent of a watched file results in "kernel BUG at
fs/notify/mark.c:139".

To reproduce

  add "-w /tmp/audit/dir/watched_file" to audit.rules
  rm -rf /tmp/audit/dir

This is caused by fsnotify_destroy_mark() being called without an
extra reference taken by the caller.

Reported by Francesco Cosoleto here:

  https://bugzilla.novell.com/show_bug.cgi?id=689860

Fix by removing the BUG_ON and adding a comment about not accessing mark after
the iput.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/notify/mark.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -135,9 +135,6 @@ void fsnotify_destroy_mark(struct fsnoti
 
 	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
 
-	/* 1 from caller and 1 for being on i_list/g_list */
-	BUG_ON(atomic_read(&mark->refcnt) < 2);
-
 	spin_lock(&group->mark_lock);
 
 	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
@@ -182,6 +179,11 @@ void fsnotify_destroy_mark(struct fsnoti
 		iput(inode);
 
 	/*
+	 * We don't necessarily have a ref on mark from caller so the above iput
+	 * may have already destroyed it.  Don't touch from now on.
+	 */
+
+	/*
 	 * it's possible that this group tried to destroy itself, but this
 	 * this mark was simultaneously being freed by inode.  If that's the
 	 * case, we finish freeing the group here.


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