Re: WARNING in ext4_invalidatepage

Theodore Y. Ts'o
2018-10-16T15:53:47Z

On Tue, Oct 16, 2018 at 04:02:07PM +0200, Dmitry Vyukov wrote:
> I am not sure how exactly this should be classified. To significant
> degree these "$FOO" discriminations are informational and only really
> affect the data format passed in.

The problem is that putting something which is simply and plainly
*wrong* is going to be actively misleading. You *have* to know what
ioctl you are trying to be trying to execute because some of them
require input data structures that you have to fill in, or that it
requires a file descriptor as opposed to an integer or a pointer to a
struct. I assume you're not just picking ioctl numbers purely at
random, right?

So I assume you had a table that said, this ioctl, 0x6611 takes a file
descriptor, and has thus-and-so-a-name. If that name is wrong, I'd
say it's pretty clearly a bug, right?

(I'll again gently point out that a tiny amount of work in making
syzkaller a tiny bit more developer toil would make it much more
effective, since all of this extra developer toil --- now I know I
can't even trust the $FOO discriminators to be right --- makes
syzkaller less scalable by pursuading developers that it's not
worthwhile to pay attention...)

> > 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. :-)

- Ted