linux-kernel - Re: [PATCH v11 2/8] pkcs7: Allow the signing algo to calculate the digest itself

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Message-ID: <CALrw=nEmPVNRvno2=48d5k+txRv=CKKezsKt5YunoKHUaNhGmQ@mail.gmail.com>
Date: Wed, 7 Jan 2026 13:59:48 +0000
From: Ignat Korchagin <ignat@...udflare.com>
To: David Howells <dhowells@...hat.com>
Cc: Lukas Wunner <lukas@...ner.de>, Jarkko Sakkinen <jarkko@...nel.org>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Eric Biggers <ebiggers@...nel.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, 
	Daniel Gomez <da.gomez@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, 
	"Jason A . Donenfeld" <Jason@...c4.com>, Ard Biesheuvel <ardb@...nel.org>, Stephan Mueller <smueller@...onox.de>, 
	linux-crypto@...r.kernel.org, keyrings@...r.kernel.org, 
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 2/8] pkcs7: Allow the signing algo to calculate the
 digest itself

On Wed, Jan 7, 2026 at 1:53 PM David Howells <dhowells@...hat.com> wrote:
>
> Ignat Korchagin <ignat@...udflare.com> wrote:
>
> > > +                       ret = -ENOMEM;
> > > +                       sig->digest = kmalloc(umax(sinfo->authattrs_len, sig->digest_size),
> > > +                                             GFP_KERNEL);
> >
> > Can we refactor this so we allocate the right size from the start.
>
> The problem is that we don't know the right size until we've tried parsing it.
>
> > Alternatively, should we just unconditionally use this approach
> > "overallocating" some times?
>
> In some ways, what I'd rather do is push the hash calculation down into the
> crypto/ layer for all public key algos.

Probably better indeed

> Also, we probably don't actually need to copy the authattrs, just retain a
> pointer into the source buffer and the length since we don't intend to keep
> the digest around beyond the verification procedure.  So I might be able to
> get away with just a flag saying I don't need to free it.
>
> However, there's an intermediate hash if there are authattrs, so I will need
> to store that somewhere - though that could be allocated on demand.
>
> David
>

Ignat