linux-kernel - Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only with a mount option

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Message-ID: <CALCETrUF4v=H-BnSF1tUbcCsr+8=as_=10HCz2122WT7euU58w@mail.gmail.com>
Date:	Tue, 21 Oct 2014 14:44:31 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Michael j Theall <mtheall@...ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	fuse-devel@...ts.sourceforge.net,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	"Serge H. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only
 with a mount option

On Tue, Oct 21, 2014 at 2:34 PM, Michael j Theall <mtheall@...ibm.com> wrote:
> Andy Lutomirski <luto@...capital.net> wrote on 10/21/2014 04:27:13 PM:
>> But how does this help with FUSE at all?   Does FUSE end up calling
>> xattr_permission?
>>
>> --Andy
>>
>
> The xattr system calls go through xattr_permission before it ever gets to
> the FUSE ops.

But a malicious FUSE filesystem can just put those xattrs there by
fiat, the same way that my old FUSE-based sploit put a setuid root
copy of bash in the filesystem.  No setxattr calls are needed.

--Andy
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