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SubjectRe: [PATCH v3 2/2] tpm: in tpm2_del_space check if ops pointer is still valid
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On Fri, 2021-02-05 at 00:50 +0100, Lino Sanfilippo wrote:
> From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
>
> In tpm2_del_space() chip->ops is used for flushing the sessions.
> However
> this function may be called after tpm_chip_unregister() which sets
> the chip->ops pointer to NULL.
> Avoid a possible NULL pointer dereference by checking if chip->ops is
> still
> valid before accessing it.
>
> Fixes: a3fbfae82b4c ("tpm: take TPM chip power gating out of
> tpm_transmit()")
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
> ---
> drivers/char/tpm/tpm2-space.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-
> space.c
> index 784b8b3..9a29a40 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -58,12 +58,17 @@ 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)) {
> - tpm2_flush_sessions(chip, space);
> - tpm_chip_stop(chip);
> + down_read(&chip->ops_sem);
> + if (chip->ops) {
> + mutex_lock(&chip->tpm_mutex);
> + if (!tpm_chip_start(chip)) {
> + tpm2_flush_sessions(chip, space);
> + tpm_chip_stop(chip);
> + }
> + mutex_unlock(&chip->tpm_mutex);
> }
> - mutex_unlock(&chip->tpm_mutex);
> + up_read(&chip->ops_sem);
> +
> kfree(space->context_buf);
> kfree(space->session_buf);
> }


Actually, this still isn't right. As I said to the last person who
reported this, we should be doing a get/put on the ops, not rolling our
own here:

https://lore.kernel.org/linux-integrity/e7566e1e48f5be9dca034b4bfb67683b5d3cb88f.camel@HansenPartnership.com/

The reporter went silent before we could get this tested, but could you
try, please, because your patch is still hand rolling the ops get/put,
just slightly better than it had been done previously.

James




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