linux-kernel - Re: [RFC PATCH] autofs: find_autofs

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Message-ID: <YEVvnvFNpfld7MXM@zeniv-ca.linux.org.uk>
Date:   Mon, 8 Mar 2021 00:28:14 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Alexander Mikhalitsyn <alexander.mikhalitsyn@...tuozzo.com>
Cc:     Ian Kent <raven@...maw.net>, Matthew Wilcox <willy@...radead.org>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, autofs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Ross Zwisler <zwisler@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Mattias Nissler <mnissler@...omium.org>,
        linux-fsdevel@...r.kernel.org, alexander@...alicyn.com
Subject: Re: [RFC PATCH] autofs: find_autofs_mount overmounted parent support

On Mon, Mar 08, 2021 at 12:12:22AM +0000, Al Viro wrote:

> 	Wait, so you have /proc overmounted, without anything autofs-related on
> /proc/sys/fs/binfmt_misc and still want to have the pathname resolved, just
> because it would've resolved with that overmount of /proc removed?
> 
> 	I hope I'm misreading you; in case I'm not, the ABI is extremely
> tasteless and until you manage to document the exact semantics you want
> for param->path, consider it NAKed.

	BTW, if that thing would be made to work, what's to stop somebody from
doing ...at() syscalls with the resulting fd as a starting point and pathnames
starting with ".."?  "/foo is overmounted, but we can get to anything under
/foo/bar/ in the underlying tree since there's an autofs mount somewhere in
/foo/bar/splat/puke/*"?

	IOW, the real question (aside of "WTF?") is what are you using the
resulting descriptor for and what do you need to be able to do with it.
Details, please.