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Date: Tue, 14 Jan 2020 08:25:19 +0800 From: Ian Kent <raven@...maw.net> To: Al Viro <viro@...iv.linux.org.uk> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Aleksa Sarai <cyphar@...har.com>, David Howells <dhowells@...hat.com>, Eric Biederman <ebiederm@...ssion.com>, stable <stable@...r.kernel.org>, Christian Brauner <christian.brauner@...ntu.com>, Serge Hallyn <serge@...lyn.com>, dev@...ncontainers.org, Linux Containers <containers@...ts.linux-foundation.org>, Linux API <linux-api@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks On Mon, 2020-01-13 at 10:59 +0800, Ian Kent wrote: > > > 3) is _anything_ besides root directory ever created in direct > > autofs > > superblocks by anyone? If not, why does autofs_lookup() even > > bother > > to > > do anything there? IOW, why not have it return ERR_PTR(-ENOENT) > > immediately > > for direct ones? Or am I missing something and it is, in fact, > > possible > > to have the daemon create something in those? > > Short answer is no, longer answer is directories "shouldn't" ever > be created inside direct mount points. > > The thing is that the multi-mount map construct can be used with > direct mounts too, but they must always have a real mount at the > base because they are direct mounts. So processes should not be > able to walk into them while they are being mounted (constructed). > > But I'm pretty sure it's rare (maybe not done at all) that this > map construct is used with direct mounts. This isn't right. There's actually nothing stopping a user from using a direct map entry that's a multi-mount without an actual mount at its root. So there could be directories created under these, it's just not usually done. I'm pretty sure I don't check and disallow this. Ian
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