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

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Message-ID: <20190618204933.GE17978@ZenIV.linux.org.uk>
Date:   Tue, 18 Jun 2019 21:49:33 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     linux-fsdevel@...r.kernel.org,
        syzbot <syzbot+0341f6a4d729d4e0acf1@...kaller.appspotmail.com>,
        jmorris@...ei.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, serge@...lyn.com,
        syzkaller-bugs@...glegroups.com, takedakn@...data.co.jp,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] tomoyo: Don't check open/getattr permission on sockets.

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?