Re: [GIT PULL] ksmbd server security fixes

[Steve French]

On Mon, Sep 20, 2021 at 5:46 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Sun, Sep 19, 2021 at 7:22 AM Steve French <smfrench@xxxxxxxxx> wrote:
> >
> > 3 ksmbd fixes: including an important security fix for path
> > processing, and a missing buffer overflow check, and a trivial fix for
> > incorrect header inclusion
> >
> > There are three additional patches (and also a patch to improve
> > symlink checks) for other buffer overflow cases that are being
> > reviewed and tested.
>
> Note that if you are working on a path basis, you should really take a
> look at our vfs lookup_flags, and LOOKUP_BENEATH in particular.

This was also something that Ralph brought up, and Namjae is looking
at now.

> The way to deal with '..' and symlinks is not to try to figure it out
> yourself. You'll get it wrong, partly because the races with rename
> are quite interesting. The VFS layer knows how to limit pathname
> lookup to the particular directory you started in these days.
>
> Of course, that is only true for the actual path lookup functions.
> Once you start doing things manually one component at a time yourself,
> you're on your own.

Agreed.  Also FYI I removed the "ksmbd: Use LOOKUP_NO_SYMLINKS"
changeset from for-next (I left the first two buffer validation changesets
in, since those have been reviewed), since Namjae is working on
an updated version following your suggestion (and others' review feedback).

-- 
Thanks,

Steve