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    SubjectRe: [PATCH/proposal] dm-crypt: add digest-based iv generation mode
    On Wed, Feb 25, 2004 at 03:25:24AM +0100, Christophe Saout wrote:
    > Am Di, den 24.02.2004 schrieb Matt Mackall um 20:11:
    >
    > > > + int tfm_size = sizeof(*cc->digest) + cc->digest->__crt_alg->cra_ctxsize;
    > > > + char tfm[tfm_size];
    > > > [...]
    > > > + memcpy(tfm, cc->digest, tfm_size);
    > >
    > > As this stands, it's rather scary.
    > >
    > > - it will quietly break when cryptoapi gets fiddled with
    >
    > Yes, and it's already broken. When putting a lot of stress to the
    > filesystem data corruption pops up.
    >
    > It turned out the hmac code uses an additional scratch pad which is used
    > in crypto_hmac_final (the "opad") which was kmalloc'ed. So it isn't even
    > inside the context (the one after struct tfm with length cra_ctxsize).
    >
    > Why that? That kmalloc could have been avoided and the opad could store
    > after the tfm struct too (or on the stack of the crypto_hmac_final or is
    > it too large?). Yes, I know, ... but it would really be nice not to put
    > locks around the calls.


    This is insine, there is no reason to have that outside of function scope at
    all.

    Here's the fix.
    http://jlcooke.ca/lkml/hmac_reent.patch

    Uses the stack now (peak stack usage will not go up)

    James - I'll wrap this one up with my other in one patch. This is a "look
    see, say 'OK'" patch.

    JLC

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