linux-kernel - Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount

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Message-ID: <20170221160649.GC28653@redhat.com>
Date:   Tue, 21 Feb 2017 11:06:49 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Theodore Tso <tytso@....edu>,
        Josh Triplett <josh@...htriplett.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Dongsu Park <dongsu@...ocode.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Alban Crequy <alban.crequy@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Phil Estes <estesp@...il.com>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount

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.

Vivek