lsm sb_delete hook, was Re: [PATCH 4/7] vfs: Convert sb->s_inodes iteration to super_iter_inodes()

[Dave Chinner]

On Thu, Oct 03, 2024 at 06:17:31PM +0200, Jan Kara wrote:
> On Thu 03-10-24 23:59:51, Dave Chinner wrote:
> > As for the landlock code, I think it needs to have it's own internal
> > tracking mechanism and not search the sb inode list for inodes that
> > it holds references to. LSM cleanup should be run before before we
> > get to tearing down the inode cache, not after....
> 
> Well, I think LSM cleanup could in principle be handled together with the
> fsnotify cleanup but I didn't check the details.

I'm not sure how we tell if an inode potentially has a LSM related
reference hanging off it. The landlock code looks to make an
assumption in that the only referenced inodes it sees will have a
valid inode->i_security pointer if landlock is enabled. i.e. it
calls landlock_inode(inode) and dereferences the returned value
without ever checking if inode->i_security is NULL or not.

I mean, we could do a check for inode->i_security when the refcount
is elevated and replace the security_sb_delete hook with an
security_evict_inode hook similar to the proposed fsnotify eviction
from evict_inodes().

But screwing with LSM instructure looks ....  obnoxiously complex
from the outside...

-Dave.
-- 
Dave Chinner
david at fromorbit.com