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

[David Howells]

Ignat Korchagin <ignat@xxxxxxxxxxxxxx> 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.

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