linux-kernel - Re: [PATCH v2 02/30] fuse: Clear setuid bit even in cache=never path

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Date:   Mon, 20 May 2019 16:44:37 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-nvdimm@...ts.01.org,
        stefanha@...hat.com, dgilbert@...hat.com, swhiteho@...hat.com
Subject: Re: [PATCH v2 02/30] fuse: Clear setuid bit even in cache=never path

On Mon, May 20, 2019 at 04:41:37PM +0200, Miklos Szeredi wrote:
> On Wed, May 15, 2019 at 03:26:47PM -0400, Vivek Goyal wrote:
> > If fuse daemon is started with cache=never, fuse falls back to direct IO.
> > In that write path we don't call file_remove_privs() and that means setuid
> > bit is not cleared if unpriviliged user writes to a file with setuid bit set.
> > 
> > pjdfstest chmod test 12.t tests this and fails.
> 
> I think better sulution is to tell the server if the suid bit needs to be
> removed, so it can do so in a race free way.
> 
> Here's the kernel patch, and I'll reply with the libfuse patch.

Here are the patches for libfuse and passthrough_ll.

View attachment "libfuse-add-fuse_write_kill_priv.patch" of type "text/plain" (2439 bytes)

View attachment "passthrough_ll-kill-suid.patch" of type "text/plain" (1825 bytes)