Re: Crypto Fixes for 4.12

From	Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: Crypto Fixes for 4.12
Date	2017-06-15 11:10 +0200
Message-ID	<tSyWR-yc-13@gated-at.bofh.it> (permalink)
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On Thu, Jun 15, 2017 at 9:54 AM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> This push fixes a bug on sparc where we may dereference freed stack
> memory.

Ugh, that's a particularly ugly fix for a random gcc bug on a random
architecture that almost nobody tests.

In other words, it's nasty. It's nasty because nobody sane will ever
realize this pattern, and the code will either bit-rot or just happen
again somewhere else.

I'd have been *much* happier if this had been some nicer abstraction
that is built up around the use of SHASH_DESC_ON_STACK(), and just
have some rule that "SHASH_DESC_ON_STACK()" needs to be paired with
retrieving the final value and then a SHASH_DESC_DEALLOC() or
whatever.

Then you *could* implement SHASH_DESC_ON_STACK() as a kmalloc, and
SHASH_DESC_DEALLOC() would be a kfree - but with an alloca()-like
allocation the SHASH_DESC_DEALLOC() would be that "barrier_data()".

At that point the interface would make _sense_ at some conceptual
level, rather than being a random hack for a small collection of
random users of this thing.

There's a fair number of SHASH_DESC_ON_STACK users, are all the others
safe for some random reason that just happens to be about code
generation? Did people actually verify that?

                Linus

Thread

Crypto Fixes for 4.12 Herbert Xu <herbert@gondor.apana.org.au> - 2017-06-08 11:30 +0200
  Re: Crypto Fixes for 4.12 David Miller <davem@davemloft.net> - 2017-06-08 16:10 +0200
    Re: Crypto Fixes for 4.12 Herbert Xu <herbert@gondor.apana.org.au> - 2017-06-09 05:00 +0200
  Crypto Fixes for 4.12 Herbert Xu <herbert@gondor.apana.org.au> - 2017-06-15 03:00 +0200
    Re: Crypto Fixes for 4.12 Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-15 11:10 +0200
      Re: Crypto Fixes for 4.12 Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-15 11:10 +0200
      Re: Crypto Fixes for 4.12 Herbert Xu <herbert@gondor.apana.org.au> - 2017-06-15 11:50 +0200
        Re: Crypto Fixes for 4.12 David Miller <davem@davemloft.net> - 2017-06-15 17:10 +0200
      Re: Crypto Fixes for 4.12 David Miller <davem@davemloft.net> - 2017-06-15 17:10 +0200
        Re: Crypto Fixes for 4.12 Theodore Ts'o <tytso@mit.edu> - 2017-06-16 15:00 +0200
          Re: Crypto Fixes for 4.12 David Miller <davem@davemloft.net> - 2017-06-16 19:00 +0200

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