linux-kernel - Re: [PATCH v5 4/4] fuse: Allow user namespace mounts

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Message-ID: <CALCETrUWt+8jfgNN-H=JkxgAcn2j1wQigaovxcmYqKx+=m9oHA@mail.gmail.com>
Date:	Wed, 22 Oct 2014 19:19:44 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Lutomirski <luto@...capital.net>,
	Miklos Szeredi <miklos@...redi.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge H. Hallyn" <serge.hallyn@...ntu.com>,
	Michael j Theall <mtheall@...ibm.com>,
	fuse-devel@...ts.sourceforge.net,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Cc:	Seth Forshee <seth.forshee@...onical.com>
Subject: Re: [PATCH v5 4/4] fuse: Allow user namespace mounts

On Wed, Oct 22, 2014 at 5:22 PM, Seth Forshee
<seth.forshee@...onical.com> wrote:
> On Wed, Oct 22, 2014 at 02:51:56PM -0700, Andy Lutomirski wrote:
>> On Wed, Oct 22, 2014 at 2:24 PM, Seth Forshee
>> <seth.forshee@...onical.com> wrote:
>> > Cc: Eric W. Biederman <ebiederm@...ssion.com>
>> > Cc: Serge H. Hallyn <serge.hallyn@...ntu.com>
>> > Cc: Andy Lutomirski <luto@...capital.net>
>> > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
>> > ---
>> >  fs/fuse/inode.c | 4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
>> > index b88b5a780228..7d0e73e36e7b 100644
>> > --- a/fs/fuse/inode.c
>> > +++ b/fs/fuse/inode.c
>> > @@ -1201,7 +1201,7 @@ static void fuse_kill_sb_anon(struct super_block *sb)
>> >  static struct file_system_type fuse_fs_type = {
>> >         .owner          = THIS_MODULE,
>> >         .name           = "fuse",
>> > -       .fs_flags       = FS_HAS_SUBTYPE,
>> > +       .fs_flags       = FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
>> >         .mount          = fuse_mount,
>> >         .kill_sb        = fuse_kill_sb_anon,
>> >  };
>> > @@ -1233,7 +1233,7 @@ static struct file_system_type fuseblk_fs_type = {
>> >         .name           = "fuseblk",
>> >         .mount          = fuse_mount_blk,
>> >         .kill_sb        = fuse_kill_sb_blk,
>> > -       .fs_flags       = FS_REQUIRES_DEV | FS_HAS_SUBTYPE,
>> > +       .fs_flags       = FS_REQUIRES_DEV | FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
>> >  };
>> >  MODULE_ALIAS_FS("fuseblk");
>> >
>> > --
>> > 1.9.1
>> >
>>
>> This is mostly a sign of my ignorance, but how does this actually end
>> up working?  I assume that the mounter opens /dev/fuse and then passes
>> the fd to the mount call.  Which userns is captured?  The opener of
>> /dev/fuse or the mounter of the fs?
>
> You're correct that the mounter passes the fd to /dev/fuse to the mount
> call. The namespace of the mounter is used, but there's also a check to
> make sure that's the same as that of the opener of /dev/fuse, otherwise
> the mount fails.

As long as my nodev fix is either applied first or rejected,

Acked-by: Andy Lutomirski <luto@...capital.net>

Although the LSM situation is still a mess.  Serge, any thoughts?

--Andy

>
> Seth



-- 
Andy Lutomirski
AMA Capital Management, LLC
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