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

From	James Bottomley <James.Bottomley@HansenPartnership.com>
Newsgroups	linux.kernel
Subject	Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount
Date	2017-02-21 23:30 +0100
Message-ID	<tdr6x-on-3@gated-at.bofh.it> (permalink)
References	<td6Ot-3u9-3@gated-at.bofh.it> <td6Ot-3u9-5@gated-at.bofh.it> <tdlaO-4Vr-23@gated-at.bofh.it>
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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

Thread

[RFC v2 0/1] shiftfs: uid/gid shifting filesystem (s_user_ns  version) James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-02-21 01:50 +0100
  [RFC v2 1/1] shiftfs: uid/gid shifting bind mount James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-02-21 01:50 +0100
    Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount Vivek Goyal <vgoyal@redhat.com> - 2017-02-21 17:10 +0100
      Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-02-21 23:30 +0100
        Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount Vivek Goyal <vgoyal@redhat.com> - 2017-02-22 17:50 +0100

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