Re: [PATCH] tomoyo: Don't check open/getattr permission on sockets.

[Al Viro <viro@zeniv.linux.org.uk>]

On Sun, Jun 16, 2019 at 03:49:00PM +0900, Tetsuo Handa wrote:
> Hello, Al.
> 
> Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk
>     management.

You do realize that sockets are not unique in that respect, right?
All kinds of interesting stuff can be accessed via /proc/*/fd/*, and
it _can_ be closed under you.  So I'd suggest checking how your code
copes with similar for pipes, FIFOs, epoll, etc., accessed that way...

We are _not_ going to be checking that in fs/open.c - the stuff found
via /proc/*/fd/* can have the associated file closed by the time
we get to calling ->open() and we won't know that until said call.

> Q2: Do you see any problem with using f->f_path.dentry->d_inode ?
>     Do we need to use d_backing_inode() or d_inode() ?

Huh?  What's wrong with file_inode(f), in the first place?  And
just when can that be NULL, while we are at it?

> >  static int tomoyo_inode_getattr(const struct path *path)
> >  {
> > +	/* It is not safe to call tomoyo_get_socket_name(). */
> > +	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
> > +		return 0;

Can that be called for a negative?