Re: [RFC 2/5 v4] procfs: add hidepid= and gid= mount options

From: James Morris
Date: Mon Jun 20 2011 - 01:09:08 EST

[please cc: the lsm list with this kind of thing]

> This patch adds support of mount options to restrict access to
> /proc/PID/ directories. The default backward-compatible 'relaxed'
> behaviour is left untouched.

Can you provide evidence that this is a useful feature? e.g. examples of
exploits / techniques which would be _usefully_ hampered or blocked.

> The first mount option is called "hidepid" and its value defines how much
> info about processes we want to be available for non-owners:
> hidepid=0 (default) means the current behaviour - anybody may read all
> world-readable /proc/PID/* files.

Why not utilize unix perms on the proc files? Perhaps via stricter
overall defaults which are selected at kernel build or runtime.

> hidepid=1 means users may not access any /proc/<pid>/ directories, but their
> own. Sensitive files like cmdline, io, sched*, status, wchan are now
> protected against other users. As permission checking done in
> proc_pid_permission() and files' permissions are left untouched,
> programs expecting specific files' permissions are not confused.

IMHO such programs are beyond broken and have voided their kernel

James Morris
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