linux-kernel - Re: [PATCH 29/38] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #10]

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <19865.1532854200@warthog.procyon.org.uk>
Date:   Sun, 29 Jul 2018 09:50:00 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 29/38] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #10]

Jann Horn <jannh@...gle.com> wrote:

> [...]
> > +       case fsconfig_set_binary:
> > +               param.type = fs_value_is_blob;
> > +               param.size = aux;
> > +               param.blob = memdup_user_nul(_value, aux);
> > +               if (IS_ERR(param.blob)) {
> > +                       ret = PTR_ERR(param.blob);
> > +                       goto out_key;
> > +               }
> > +               break;
> 
> This means that a namespace admin (iow, an unprivileged user) can
> allocate 1MB of unswappable kmalloc memory per userspace task, right?
> Using userfaultfd or FUSE, you can then stall the task as long as you
> want while it has that allocation. Is that problematic, or is that
> normal?

That's not exactly the case.  A userspace task can make a temporary
allocation, but unless the filesystem grabs it, it's released again on exit
from the system call.

Note that I should probably use vmalloc() rather than kmalloc(), but that
doesn't really affect your point.  I could also pass the user pointer through
to the filesystem instead - I wanted to avoid that for this interface, but it
make sense in this instance.

David