linux-kernel - [PATCH] autofs4: fix race in unhashed dentry code

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Date:	Wed, 11 Apr 2007 11:05:29 -0400
From:	Jeff Mahoney <jeffm@...e.com>
To:	Ian Kent <raven@...maw.net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>
Subject: [PATCH] autofs4: fix race in unhashed dentry code

 Commit f50b6f8691cae2e0064c499dd3ef3f31142987f0 introduced a
 race in autofs4 between autofs_lookup_unhashed() and
 autofs_dentry_release().

 autofs_dentry_release() ends up clearing the ->dentry and ->inode
 members of autofs_info before removing it from the rehash list. The
 list is protected by the rehash lock in both functions, but
 since autofs_dentry_release() starts tearing the autofs_info struct
 down before removing it from the list, autofs_lookup_unhashed() can
 get a autofs_info with a NULL dentry.

 This patch moves the clearing of ->dentry and ->inode after the removal
 from the rehash list.

Signed-off-by: Jeff Mahoney <jeffm@...e.com>

---

 fs/autofs4/root.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/autofs4/root.c	2007-04-11 09:41:44.000000000 -0400
+++ b/fs/autofs4/root.c	2007-04-11 10:54:37.000000000 -0400
@@ -470,9 +470,6 @@ void autofs4_dentry_release(struct dentr
 	if (inf) {
 		struct autofs_sb_info *sbi = autofs4_sbi(de->d_sb);

-		inf->dentry = NULL;
-		inf->inode = NULL;
-
 		if (sbi) {
 			spin_lock(&sbi->rehash_lock);
 			if (!list_empty(&inf->rehash))
@@ -480,6 +477,9 @@ void autofs4_dentry_release(struct dentr
 			spin_unlock(&sbi->rehash_lock);
 		}

+		inf->dentry = NULL;
+		inf->inode = NULL;
+
 		autofs4_free_ino(inf);
 	}
 }

-- 
Jeff Mahoney
SUSE Labs
-
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