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Date: Thu, 15 Feb 2007 13:23:40 +0900 (WST)
From: Ian Kent <raven@themaw.net>
To: Andrew Morton <akpm@osdl.org>
cc: Kernel Mailing List <linux-kernel@vger.kernel.org>, autofs mailing list <autofs@linux.kernel.org>
Subject: [PATCH 2/2] autofs4 - check for directory re-create in lookup
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Hi Andrew,
This problem was identified and fixed some time ago by Jeff Moyer
but it fell through the cracks somehow.
It is possible that a user space application could remove and
re-create a directory during a request. To avoid returning a
failure from lookup incorrectly when our current dentry is
unhashed we need to check if another positive, hashed dentry
matching this one exists and if so return it instead of a fail.
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Ian
---
--- linux-2.6.20/fs/autofs4/root.c.lookup-check-unhased 2007-02-12 13:49:46.000000000 +0900
+++ linux-2.6.20/fs/autofs4/root.c 2007-02-12 13:54:58.000000000 +0900
@@ -655,14 +655,29 @@ static struct dentry *autofs4_lookup(str
/*
* If this dentry is unhashed, then we shouldn't honour this
- * lookup even if the dentry is positive. Returning ENOENT here
- * doesn't do the right thing for all system calls, but it should
- * be OK for the operations we permit from an autofs.
+ * lookup. Returning ENOENT here doesn't do the right thing
+ * for all system calls, but it should be OK for the operations
+ * we permit from an autofs.
*/
if (dentry->d_inode && d_unhashed(dentry)) {
+ /*
+ * A user space application can (and has done in the past)
+ * remove and re-create this directory during the callback.
+ * This can leave us with an unhashed dentry, but a
+ * successful mount! So we need to perform another
+ * cached lookup in case the dentry now exists.
+ */
+ struct dentry *parent = dentry->d_parent;
+ struct dentry *new = d_lookup(parent, &dentry->d_name);
+ if (new != NULL)
+ dentry = new;
+ else
+ dentry = ERR_PTR(-ENOENT);
+
if (unhashed)
dput(unhashed);
- return ERR_PTR(-ENOENT);
+
+ return dentry;
}
if (unhashed)
-
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