On Tue, Apr 24, 2018 at 12:58 PM, Serge E. Hallyn [off-list ref] wrote:

Quoting Tycho Andersen (tycho at tycho.ws):

quoted

On Tue, Apr 24, 2018 at 11:46:38PM +0900, Tetsuo Handa wrote:

quoted

Tycho Andersen wrote:

quoted

quoted

quoted

+     if (unlikely(crypto_aead_ivsize(big_key_aead) != GCM_AES_IV_SIZE)) {
+             WARN(1, "big key algorithm changed?");

Please avoid using WARN() WARN_ON() etc.
syzbot would catch it and panic() due to panic_on_warn == 1.

But it is really a programming bug in this case (and it seems better
than BUG()...). Isn't this exactly the sort of case we want to catch?

Tycho

Right - is there a url to some discussion about this?  Because not
using WARN when WARN should be used, because it troubles a bot, seems
the wrong solution.  If this *is* what's been agreed upon, then
what is the new recommended thing to do here?

BUG() is basically supposed to never be used, as decreed by Linus.
WARN() here is entirely correct: if we encounter a case where
crypto_aead_ivsize(big_key_aead) != GCM_AES_IV_SIZE is not true, we
run the risk of stack memory corruption. If this is an EXPECTED
failure case, then okay, drop the WARN() but we have to keep the
-EINVAL.

-Kees

-- 
Kees Cook
Pixel Security
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