# Re: \[PATCH v5 1/1\] tpm: add sysfs exports for all banks of PCR registers

- From: James Bottomley \<James.Bottomley@HansenPartnership.com\>
- Date: 2021-01-15 18:05:40 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/01/13329995
- Thread: https://ratatoskr.run/linux-integrity/2021/01/13329974/t.md

```text
[separate reply because the asked about part isn't in my patch it's in
existing code]

On Wed, 2021-01-13 at 08:50 +0100, Greg KH wrote:
> On Tue, Jan 12, 2021 at 05:59:58PM -0800, James Bottomley wrote:
[...]
> >  void tpm_sysfs_add_device(struct tpm_chip *chip)
> >  {
> > +	int i;
> > +
> >  	WARN_ON(chip->groups_cnt != 0);
> > +
> 
> How can that WARN_ON happen?

If tpm_sysfs_add_device gets called more than once, say because reuse
of the chip structure that causes it to be initialized again without
properly being torn down.  I think it's a reasonable assert given that
we'll run off the end of the chip->groups array if it isn't true ...
which does really argue it should be a BUG_ON because the machine will
be compromised and likely unrecoverable if it triggers.

James


```