Re: [PATCH 2/2] tpm: Fix crash on tmprm release

[Stefan Berger <stefanb@linux.ibm.com>]

On 6/15/21 05:14, Vincent Whitchurch wrote:
> If the tpm_tis module is removed (or a system shutdown is triggered)
> while the tpmrm device is use, the kernel crashes due to chip->ops being
> NULL:
>
>   # exec 3<>/dev/tpmrm0
>   # rmmod tpm_tis
>   # exit
>   ==================================================================
>   BUG: KASAN: null-ptr-deref in tpm_chip_start+0x2d/0x120 [tpm]
>   Read of size 8 at addr 0000000000000060 by task sh/994
>
>   Call Trace:
>    kasan_report.cold.13+0x10f/0x111
>    tpm_chip_start+0x2d/0x120 [tpm]
>    tpm2_del_space+0x2c/0xa0 [tpm]
>    tpmrm_release+0x3f/0x50 [tpm]
>    __fput+0x110/0x3c0
>    task_work_run+0x94/0xd0
>    do_exit+0x683/0x13e0
>    do_group_exit+0x8b/0x140
>    do_syscall_64+0x3c/0x80
>   ==================================================================
>
> Fix this by making tpm2_del_space() use tpm_try_get_ops().  The latter
> already includes the calls to tpm_chip_start() and tpm_chip_stop().
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>


As a follow-up to this message here: https://lkml.org/lkml/2022/3/1/552


Tested-by: Stefan Berger <stefanb@linux.ibm.com>




> ---
>   drivers/char/tpm/tpm2-space.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 784b8b3cb903..e1111261021f 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -58,12 +58,10 @@ 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)) {
>   		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);
>   }