Re: [PATCH 5.10] overflow.h: use new generic division helpers to avoid / operator

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kees Cook <keescook@chromium.org>,
	Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Sasha Levin <sashal@kernel.org>,
	llvm@lists.linux.dev, stable <stable@vger.kernel.org>,
	Arnd Bergmann <arnd@kernel.org>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 5.10] overflow.h: use new generic division helpers to avoid / operator
Date: Tue, 14 Sep 2021 12:57:42 -0700	[thread overview]
Message-ID: <CAHk-=whmcqmpPJQrAw4vX-Z6ePjeydjw7s6tzqzvB=uBp0=6fw@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdk9yqEMLTAxgZNmHgRSww0AnJ-x9qd7HK3v2Vepi1BdLw@mail.gmail.com>

On Tue, Sep 14, 2021 at 12:50 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> Just making sure __ffs() works as expected should blksize > LONG_MAX
> on 32b targets.  I don't see the range check you're referring to.
> loff_t is a long long, yeah?

Christ Nick.

Stop wasting my time.

Read the patch:

        if (!blksize)
-               blksize = NBD_DEF_BLKSIZE;
+               blksize = 1u << NBD_DEF_BLKSIZE_BITS;
        if (blksize < 512 || blksize > PAGE_SIZE || !is_power_of_2(blksize))
                return -EINVAL;

        nbd->config->bytesize = bytesize;
-       nbd->config->blksize = blksize;
+       nbd->config->blksize_bits = __ffs(blksize);

See that range check?

Seriously, I've now replied several times to you just because you were
too damn lazy to just look three lines up from the __ffs() that you
reacted to, when I explicitly mentioned the range check several times,
including in the original submission, and when it was RIGHT THERE IN
THE PATCH IN THE ONLY PLACE THAT DID THAT __FFS.

(Ok, so the lower check of range was 512, not 1024, sue me).

It was all there in the diff all the time.

Don't email me again about this. At least not without spending the
FIVE SECONDS to look at what the hell you are emailing me about.

           Linus