linux-ext4 - Re: [RFC] open_by_handle() vs. EA inodes

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Message-ID: <701debe87eff185064f3cc31f9a9b425cdf8fe61.camel@hammerspace.com>
Date:   Fri, 29 Jun 2018 19:38:30 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>
CC:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC] open_by_handle() vs. EA inodes

On Fri, 2018-06-29 at 19:19 +0100, Al Viro wrote:
> 	On ea_inode-enabled ext4 open_by_handle() (as well as knfsd,
> etc.)
> can get to EA inodes as long as it knows their inumbers - just pass
> it
> an fhandle with zeroed version bytes and the right inumber in it.
> 
> 	AFAICS, it's Not Nice(tm), especially since you can write to
> those,
> whether they are shared or not.
> 
> 	Should we make ext4_nfs_get_inode() check for EXT4_EA_INODE_FL
> and fail if it's set?

handle_to_path() requires CAP_DAC_READ_SEARCH capabilities. Isn't that
sufficiently restrictive for open_by_handle()?

Concerning knfsd, people can in theory enable subtree checking to
enforce checking whether or not you are in an exported subtree. In
practice that breaks rename, so people are strongly encouraged to
disable subtree checking, and only to export complete filesystems.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com