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@xxxxxxxxxxxxx> wrote:
> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> > Cc: Serge H. Hallyn <serge.hallyn@xxxxxxxxxx>
> > Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> > Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
> > ---
> > 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.
Seth
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