Re: [fuse-devel] fusexmp does not deal nicely with /dev/null

[Miklos S. <mi...@sz...>]

On Wed, 3 Dec 2008, Ole Tange wrote:
> On Wed, Oct 8, 2008 at 1:50 PM, Miklos Szeredi <mi...@sz...> wrote:
> 
> > Try the '-odev' option.  The default is 'nodev', which means devices
> > won't work.
> 
> That did not help if the mount is run by me. I still cannot write to
> root/dev/null:
> 
> + sudo rm -f /tmp/nonexisting-file
> + sudo rm -f /tmp/owned-by-root
> + mkdir -p root
> + ./fusexmp root -o allow_other,default_permissions,dev
> + touch /tmp/existing
> + touch root/tmp/existing
> + touch root/tmp/nonexisting-file
> + ls -l /tmp/nonexisting-file
> -rw-r--r-- 1 tange tange 0 2008-12-03 07:45 /tmp/nonexisting-file
> + rm -f root/tmp/nonexisting-file
> + sudo touch root/tmp/owned-by-root
> + ls -l /tmp/owned-by-root
> -rw-r--r-- 1 tange tange 0 2008-12-03 07:45 /tmp/owned-by-root
> + ls -ld root/tmp
> drwxrwxrwt 11 root root 16384 2008-12-03 07:45 root/tmp
> + ls -ld /tmp
> drwxrwxrwt 11 root root 16384 2008-12-03 07:45 /tmp
> + bash -c 'echo > /dev/null'
> + bash -c 'echo > root/dev/null'
> bash: root/dev/null: Permission denied

Allowing this would be a grave security hole (try thinking /dev/hda
in place of /dev/null).

> If the mount is run by root I cannot remove a file I just created as
> it will be owned by root:

Yes, fusexmp isn't meant to be used this way: it doesn't set file
ownership properly on creation, etc...

Miklos