[patch 07/10] unprivileged mounts: add sysctl tunable for "safe" property

[Miklos Szeredi]

> > > What do you think about doing this only if FS_SAFE is also set,
> > > so for instance at first only FUSE would allow itself to be
> > > made user-mountable?
> > > 
> > > A safe thing to do, or overly intrusive?
> > 
> > It goes somewhat against the "no policy in kernel" policy ;).  I think
> > the warning in the documentation should be enough to make sysadmins
> > think twice before doing anything foolish:
> 
> Warning in which documentation?  A sysadmin considering setting fs_safe
> for ext2 or xfs isn't going to be looking at fuse docs, which I think is
> what you're talking about.  Are you going to add a file under
> Documentation/filesystems?

Yes, I meant documentation of the new sysctl tunable in
Documentation/filesystems/proc.txt:

> Index: linux/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux.orig/Documentation/filesystems/proc.txt	2008-01-16 13:25:07.000000000 +0100
> +++ linux/Documentation/filesystems/proc.txt	2008-01-16 13:25:09.000000000 +0100
> @@ -43,6 +43,7 @@ Table of Contents
>    2.13	/proc/<pid>/oom_score - Display current oom-killer score
>    2.14	/proc/<pid>/io - Display the IO accounting fields
>    2.15	/proc/<pid>/coredump_filter - Core dump filtering settings
> +  2.16	/proc/sys/fs/types - File system type specific parameters
>  
>  ------------------------------------------------------------------------------
>  Preface
> @@ -2283,4 +2284,21 @@ For example:
>    $ echo 0x7 > /proc/self/coredump_filter
>    $ ./some_program
>  
> +2.16 /proc/sys/fs/types/ - File system type specific parameters
> +----------------------------------------------------------------
> +
> +There's a separate directory /proc/sys/fs/types/<type>/ for each
> +filesystem type, containing the following files:
> +
> +usermount_safe
> +--------------
> +
> +Setting this to non-zero will allow filesystems of this type to be
> +mounted by unprivileged users (note, that there are other
> +prerequisites as well).
> +
> +Care should be taken when enabling this, since most
> +filesystems haven't been designed with unprivileged mounting
> +in mind.
> +
>  ------------------------------------------------------------------------------
> 

Do you think this is enough?  Or do we need something more, to prevent
sysadmin inadvertently setting this for an unsafe filesystem?

Thanks,
Miklos