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    SubjectRe: [PATCH 1/3] big key: get rid of stack array allocation
    On Tue, Apr 24, 2018 at 12:58 PM, Serge E. Hallyn <serge@hallyn.com> wrote:
    > Quoting Tycho Andersen (tycho@tycho.ws):
    >> On Tue, Apr 24, 2018 at 11:46:38PM +0900, Tetsuo Handa wrote:
    >> > Tycho Andersen wrote:
    >> > > > > + 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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