Re: [PATCH] X.509: Fix crash caused by NULL pointer

[Tianjia Zhang]

On 1/7/21 6:58 PM, David Howells wrote:
> Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx> wrote:
>
> > On the following call path, `sig->pkey_algo` is not assigned
> > in asymmetric_key_verify_signature(), which causes runtime
> > crash in public_key_verify_signature().
> >
> >    keyctl_pkey_verify
> >      asymmetric_key_verify_signature
> >        verify_signature
> >          public_key_verify_signature
> >
> > This patch simply check this situation and fixes the crash
> > caused by NULL pointer.
> >
> > Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
> > Cc: stable@xxxxxxxxxxxxxxx # v5.10+
> > Reported-by: Tobias Markus <tobias@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
>
> Looks reasonable:
>
> Acked-by: David Howells <dhowells@xxxxxxxxxx>
>
> I wonder, though, if cert_sig_digest_update() should be obtained by some sort
> of function pointer.  It doesn't really seem to belong in this file.  But this
> is a separate issue.
>
> David

Yes, this is indeed the logic of the SM2 module. I have tried to 
dynamically load and obtain the pointer of this function through 
`request_module` before, but this method still does not seem very 
suitable. Here are some unfinished codes I tried before:

https://github.com/uudiin/linux/commit/55bca48c6282415d94c53a7692622d544da99342

It would be great if you have some good experience to share with me, I 
will continue to try to optimize this code.

Best regards,
Tianjia