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Subject: Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Djalal Harouni <tixxdz@gmail.com>, Chris Mason <clm@fb.com>,
        Theodore Tso <tytso@mit.edu>, Josh Triplett <josh@joshtriplett.org>,
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        linux-security-module@vger.kernel.org,
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        David Herrmann <dh.herrmann@googlemail.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Alban Crequy <alban.crequy@gmail.com>,
        Al Viro <viro@ZenIV.linux.org.uk>,
        "Serge E. Hallyn" <serge@hallyn.com>, Phil Estes <estesp@gmail.com>,
        Amir Goldstein <amir73il@gmail.com>
Date: Tue, 21 Feb 2017 17:23:26 -0500
In-Reply-To: <20170221160649.GC28653@redhat.com>
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On Tue, 2017-02-21 at 11:06 -0500, Vivek Goyal wrote:
> On Mon, Feb 20, 2017 at 04:47:05PM -0800, James Bottomley wrote:
> 
> [..]
> > +static struct dentry *shiftfs_lookup(struct inode *dir, struct
> > dentry *dentry,
> > +				     unsigned int flags)
> > +{
> > +	struct dentry *real = dir->i_private, *new;
> > +	struct inode *reali = real->d_inode, *newi;
> 
> newi needs to be initialized to NULL. Otherwise if a file does not
> exist, we try to call d_splice_alias() with uninitialized value of
> newi.
> 
> This crashes for the new file creation case.

I think you've still got an older version.  The code around that region
should read:

	

	oldcred = shiftfs_new_creds(&newcred, dentry->d_sb);
	new = lookup_one_len(dentry->d_name.name, real, dentry->d_name.len);
	shiftfs_old_creds(oldcred, &newcred);
	inode_unlock(reali);

	if (IS_ERR(new))
		return new;

	dentry->d_fsdata = new;

	newi = NULL;
	if (!new->d_inode)
		goto out;

	newi = shiftfs_new_inode(dentry->d_sb, new->d_inode->i_mode, new);
	if (!newi) {
		dput(new);
		return ERR_PTR(-ENOMEM);
	}

 out:
	return d_splice_alias(newi, dentry);

So newi is set to NULL before out is taken.  I checked: this hunk did make it to the v2 patch.

James