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

[Andy Lutomirski]

> On Jul 11, 2018, at 12:22 AM, David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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?  Youâre okay as long as *every single fs* gets it right, but thatâs
>> asking a lot.
>
> Do note that you must already have CAP_SYS_ADMIN to be able to call fsopen().

If youâre not allowing it already, someone will want user namespace
root to be able to use this very, very soon.