Re: [GIT PULL] Asymmetric keys fix for v6.4-rc5

[Eric Biggers]

On Sat, Jun 03, 2023 at 12:41:00PM +0200, Roberto Sassu wrote:
> On 6/3/2023 2:02 AM, Linus Torvalds wrote:
> > On Fri, Jun 2, 2023 at 1:38 PM Linus Torvalds
> > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > 
> > > The patch re-uses the allocation it already does for the key data, and
> > > it seems sane.
> > 
> > Ugh. I had to check that it was ok to re-use the key buffer, but it
> > does seem to be the case that you can just re-use the buffer after
> > you've done that crypto_akcipher_set_priv/pub_key() call, and the
> > crypto layer has to copy it into its own data structures.
> 
> Yes, we could not do it if the set_pub_key/set_priv_key methods use
> internally the passed pointer. I guess it depends on the methods, for RSA
> and ECDSA it seems fine (they copy to a different location).
> 
> The doubt comes because the buffer is freed after crypto_wait_req() and not
> after crypto_akcipher_set_*_key(), suggesting that it could be actually used
> during the crypto operation.
> 
> Rechecked the thread, and the suggestion to reuse the buffer and not append
> the signature and digest at the end was by Eric Biggers.
> 
> Eric, in light of this finding, should we still reuse the buffer?
> 

I don't think there was any "finding" here.  The setkey methods in the crypto
API aren't allowed to reuse the buffer they are passed, so the patch is fine.

- Eric