linux-kernel - Re: [PATCH 05/14] fs: don't allow kernel reads and writes without iter ops

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Date:   Fri, 9 Oct 2020 18:29:13 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Eric Biggers <ebiggers@...nel.org>,
        Alexander Viro <aviro@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 05/14] fs: don't allow kernel reads and writes without
 iter ops

On Fri, Oct 9, 2020 at 6:19 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> Okay, that makes more sense.  So the patchset from Matthew
> https://lkml.kernel.org/linux-fsdevel/20201003025534.21045-1-willy@infradead.org/T/#u
> isn't what you had in mind.

No.

That first patch makes sense - it's just the "ppos can be NULL" patch.

But as mentioned, NULL isn't "shorthand for zero". It's just "pipes
don't _have_ a pos, trying to pass in some explicit position is
crazy".

So no, the other patches in that set are a bit odd, I think.

SOME of them look potentially fine - the bpfilter one seems to be
valid, for example, because it's literally about reading/writing a
pipe. And maybe the sysctl one is similarly sensible - I didn't check
the context of that one.

But no, NULL shouldn't mean "start at position zero, and we don't care
about the result".

              Linus