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[Dazuko-devel] Bug in stackable filesystems like wrapfs, ecryptfs etc.

From: Lino Sanfilippo
Subject: [Dazuko-devel] Bug in stackable filesystems like wrapfs, ecryptfs etc.
Date: Thu, 18 Jun 2009 18:27:35 +0200
User-agent: Icedove (X11/20090105)


our company is working with the stackable filesystem dazukofs that is based on wrapfs from the FiST

We discovered a bug in the case that a stackable filesystem like ecryptfs, wrapfs or dazukofs, is stacked upon itself, i.e by mounting it several times at the same mount point.

An access to a file (i.e. by touching it) through 3 or more layers of one of those stackable filesystems,
results in an Oops.
The reason is the usage of the lookup_one_len() function, which passes a NULL nameidata to the lower filesystem if it has the d_revalidate() dentry operation defined.

Thus, stackable filesystem like wrapfs, ecryptfs and dazukofs assume that the filesystem below it handles
NULL values for the nameidata correctly, which might not be true:

Ironically these stackable filesystems themselves, are not prepared to handle those NULL values. So if the underlaying filesystem is one of those stackable filesystems, it might try to access the nameidata struct and the Oops occurs due to the access of a NULL pointer.

So I would like to know:
Are there any concerns with replacing the lookup_one_len() function with vfs_lookup()
to avoid the problem of the NULL nameidata?

Thx in advance and
best regards,



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