Re: [PATCH v1] usb: typec: tcpm: Check for port partner validity before consuming it

[Dmitry Baryshkov]

On Sat, Apr 27, 2024 at 05:50:10PM +0000, Badhri Jagan Sridharan wrote:
> typec_register_partner() does not guarantee partner registration
> to always succeed. In the event of failure, port->partner is set
> to the error value or NULL. Given that port->partner validity is
> not checked, this results in the following crash:
> 
> [17514.377076][  T275] Unable to handle kernel NULL pointer dereference at virtual address 00000000000003c0
> [17514.378270][  T275] pc : run_state_machine+0x1bc8/0x1c08
> [17514.378286][  T275] lr : run_state_machine+0x1b90/0x1c08
> ..
> [17514.378377][  T275] Call trace:
> [17514.378381][  T275]  run_state_machine+0x1bc8/0x1c08
> [17514.378388][  T275]  tcpm_state_machine_work+0x94/0xe4
> [17514.378396][  T275]  kthread_worker_fn+0x118/0x328
> [17514.378406][  T275]  kthread+0x1d0/0x23c
> [17514.378412][  T275]  ret_from_fork+0x10/0x20

Nit: thre is little use in the timestamps and the T275 tag. In future
patches you can safely ommit such data.

> 
> To prevent the crash, check for port->partner validity before
> derefencing it in all the call sites.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: c97cd0b4b54e ("usb: typec: tcpm: set initial svdm version based on pd revision")
> Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index ab6ed6111ed0..8a4fa8d875c6 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -4,7 +4,6 @@
>   *
>   * USB Power Delivery protocol stack.
>   */
> -
>  #include <linux/completion.h>
>  #include <linux/debugfs.h>
>  #include <linux/device.h>
> @@ -1580,7 +1579,8 @@ static void svdm_consume_identity(struct tcpm_port *port, const u32 *p, int cnt)
>  	port->partner_ident.cert_stat = p[VDO_INDEX_CSTAT];
>  	port->partner_ident.product = product;
>  
> -	typec_partner_set_identity(port->partner);
> +	if (!IS_ERR_OR_NULL(port->partner))

I think that it might be better to check typec_register_partner() result
in tcpm_typec_connect() and skip setting port->partner in case it
returned an error (an error message would be also beneficial).
See for example, how this is handled in ucsi_register_partner().

Then these checks can be turned into simple `if (port->partner)`.

> +		typec_partner_set_identity(port->partner);
>  
>  	tcpm_log(port, "Identity: %04x:%04x.%04x",
>  		 PD_IDH_VID(vdo),
> @@ -1742,6 +1742,9 @@ static void tcpm_register_partner_altmodes(struct tcpm_port *port)
>  	struct typec_altmode *altmode;
>  	int i;
>  
> +	if (IS_ERR_OR_NULL(port->partner))
> +		return;
> +
>  	for (i = 0; i < modep->altmodes; i++) {
>  		altmode = typec_partner_register_altmode(port->partner,
>  						&modep->altmode_desc[i]);
> @@ -4244,7 +4247,8 @@ static void tcpm_typec_connect(struct tcpm_port *port)
>  		port->partner = typec_register_partner(port->typec_port,
>  						       &port->partner_desc);
>  		port->connected = true;
> -		typec_partner_set_usb_power_delivery(port->partner, port->partner_pd);
> +		if (!IS_ERR_OR_NULL(port->partner))
> +			typec_partner_set_usb_power_delivery(port->partner, port->partner_pd);
>  	}
>  }
>  
> @@ -4323,8 +4327,10 @@ static void tcpm_typec_disconnect(struct tcpm_port *port)
>  	port->plug_prime = NULL;
>  	port->cable = NULL;
>  	if (port->connected) {
> -		typec_partner_set_usb_power_delivery(port->partner, NULL);
> -		typec_unregister_partner(port->partner);
> +		if (!IS_ERR_OR_NULL(port->partner)) {
> +			typec_partner_set_usb_power_delivery(port->partner, NULL);
> +			typec_unregister_partner(port->partner);
> +		}
>  		port->partner = NULL;
>  		port->connected = false;
>  	}
> @@ -4549,6 +4555,9 @@ static enum typec_cc_status tcpm_pwr_opmode_to_rp(enum typec_pwr_opmode opmode)
>  
>  static void tcpm_set_initial_svdm_version(struct tcpm_port *port)
>  {
> +	if (IS_ERR_OR_NULL(port->partner))
> +		return;
> +
>  	switch (port->negotiated_rev) {
>  	case PD_REV30:
>  		break;
> 
> base-commit: 3f12222a4bebeb13ce06ddecc1610ad32fa835dd
> -- 
> 2.44.0.769.g3c40516874-goog
> 

-- 
With best wishes
Dmitry