Re: [PATCH v2] tpm: Rework open/close/shutdown to avoid races

Jarkko Sakkinen
2022-03-07T16:46:14Z

On Mon, Mar 07, 2022 at 06:44:17PM +0200, Jarkko Sakkinen wrote:
> On Mon, Mar 07, 2022 at 11:22:27AM -0500, James Bottomley wrote:
> > On Mon, 2022-03-07 at 17:41 +0200, Jarkko Sakkinen wrote:
> > [...]
> > > James, would it possible for you to construct a proper patch from
> > > this and send it so we could include it to the next PR (use my tree
> > > as baseline)?
> >
> > Sure, There's not really any identifiable patch for a fixes tag, since
> > the race really always existed.
> >
> > How about the below.
> >
> > James
> >
> > -------------------8>8>8><8<8<8------------------
> >
> > From 3e0e640e47e5728b68693c5d45bf3cdd0bff48ca Mon Sep 17 00:00:00 2001
> > From: James Bottomley <James.Bottomley@HansenPartnership.com>
> > Date: Mon, 7 Mar 2022 11:16:55 -0500
> > Subject: [PATCH] tpm: use try_get_ops() in tpm-space.c
> >
> > As part of the series conversion to remove nested TPM operations:
> >
> > https://lore.kernel.org/all/20190205224723.19671-1-jarkko.sakkinen@linux.intel.com/
> >
> > exposure of the chip->tpm_mutex was removed from much of the upper
> > level code. In this conversion, tpm2_del_space() was missed. This
> > didn't matter much because it's usually called closely after a
> > converted operation, so there's only a very tiny race window where the
> > chip can be removed before the space flushing is done which causes a
> > NULL deref on the mutex. However, there are reports of this window
> > being hit in practice, so fix this by converting tpm2_del_space() to
> > use tpm_try_get_ops(), which performs all the teardown checks before
> > acquring the mutex.
> >
> > Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> > ---
> > drivers/char/tpm/tpm2-space.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> > index 265ec72b1d81..ffb35f0154c1 100644
> > --- a/drivers/char/tpm/tpm2-space.c
> > +++ b/drivers/char/tpm/tpm2-space.c
> > @@ -58,12 +58,12 @@ int tpm2_init_space(struct tpm_space *space, unsigned int buf_size)
> >
> > void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space)
> > {
> > - mutex_lock(&chip->tpm_mutex);
> > - if (!tpm_chip_start(chip)) {
> > +
> > + if (tpm_try_get_ops(chip) == 0) {
> > tpm2_flush_sessions(chip, space);
> > - tpm_chip_stop(chip);
> > + tpm_put_ops(chip);
> > }
> > - mutex_unlock(&chip->tpm_mutex);
> > +
> > kfree(space->context_buf);
> > kfree(space->session_buf);
> > }
> > --
> > 2.34.1
> >
> >
>
> Thank you! LGTM.
>
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
>
> BR, Jarkko

If possible, can you send this an identifiable patch (separate email)
with my reviewed-by applied, and I'll take it from there (i.e. it's
then available all trackers such patchwork etc.)?

BR, Jarkko