linux-kernel - Re: [PATCH] fs: call security_d_instantiate in d_obtain

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Date:	Fri, 19 Nov 2010 11:42:36 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	David Quigley <merlin@...ntercultured.net>
Cc:	Eric Paris <eparis@...hat.com>, Josef Bacik <josef@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	sds@...ho.nsa.gov, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org,
	Miklos Szeredi <miklos@...redi.hu>,
	Steve French <sfrench@...ba.org>
Subject: Re: [PATCH] fs: call security_d_instantiate in d_obtain_alias

On Fri, Nov 19, 2010 at 12:28:09AM -0500, David Quigley wrote:
> [snip]
> >If you have persistent xattr support we need the dentry since the xattr
> >code requires a dentry.  I have no idea why but that's what
> >inode->i_op->getxattr() requires.
> >
> 
> The original reason that the xattr operations take dentries is
> because of p9fs and CIFS. CIFS uses the name of the file to grab the
> extended attributes and so does p9fs. I had tried to remove this a
> while ago but couldn't find a way around that.

Both CIFS and FUSE are NFS-exportable, so both allow lookup by
filehandle, so neither can count on getting a filename at this point.

So, out of curiosity, do we know what will happen when selinux asks one
of them for an xattr on a DCACHE_DISCONNECTED dentry?

> When trying to find a
> solution I also got push back from Miklos (FUSE) as he views a
> filesystem being able to make xattr decisions based on the path name
> being a valid use-case.

So selinux may initialize an inode differently depending on which
pathname it happened to be looked up under first?

Factoring the name into the xattr return sounds scary to me.

--b.
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