linux-kernel - Re: WARNING in ext4

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] [day] [month] [year] [list]

Message-ID: <CACT4Y+b3rujNu+kJFaEmZzwOWSHuFYpYVJ4q3vvY62FtQ8+7xA@mail.gmail.com>
Date:   Tue, 30 Oct 2018 13:16:11 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+85da7ac734f7ba432ee4@...kaller.appspotmail.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING in ext4_invalidatepage

On Tue, Oct 16, 2018 at 5:53 PM, Theodore Y. Ts'o <tytso@....edu> wrote:
>> > The patch I referenced in my previous e-mail protects against
>> > additional scenarios where someone might be trying to punch a whole
>> > into a file that is being swapped into the bootloader ioctl.  This
>> > particular ioctl isn't yet being used by anyone, so it had some other
>> > issues as well, such as not interacting well with inline_data-enabled
>> > file systems --- not that any bootloader would be small enough that it
>> > would fit in an inline_data inode, but we're basically proofing the
>> > code against a malicious (or buggy) root-privileged program... such as
>> > syzbot.  :-)
>>
>> ... or paving the way to opening all of this to non-root users. Why
>> not if not bugs? ;)
>
> The intent behind this particular ioctl is used to install a boot
> loader.  It will *never* be opened to non-root users.  It doesn't even
> make sense to make it available to pseudo-containers-root users.  :-)

But it does not have to be executed on the root fs, right? Or is it?
For example, if I need to build a bootable image (which I actually
need to do for syzkaller). In the end it boils down to just creating a
local, private file with some particular contents. Should be nobody's
business, right? But for some reason on Linux creation of a local file
requires root privileges multiple times along the way. As the result I
have run the whole service as root, degrading overall security. And I
can't say that I fully trust all code and data involved, but Linux
simply does not give me any choice.