linux-kernel - Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

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Date:   Wed, 11 Jul 2018 08:22:41 +0100
From:   David Howells <dhowells@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        jannh@...gle.com
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

Andy Lutomirski <luto@...capital.net> wrote:

> >    sfd = fsopen("ext4", FSOPEN_CLOEXEC);
> >    write(sfd, "s /dev/sdb1"); // note I'm ignoring write's length arg
> 
> Imagine some malicious program passes sfd as stdout to a setuid
> program. That program gets persuaded to write "s /etc/shadow".  What
> happens?  You’re okay as long as *every single fs* gets it right, but that’s
> asking a lot.

Do note that you must already have CAP_SYS_ADMIN to be able to call fsopen().

David