[v2] usb: typec: tcpm: Check for port partner validity before consuming it

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:

Unable to handle kernel NULL pointer dereference at virtual address 00000000000003c0
 pc : run_state_machine+0x1bc8/0x1c08
 lr : run_state_machine+0x1b90/0x1c08
..
 Call trace:
   run_state_machine+0x1bc8/0x1c08
   tcpm_state_machine_work+0x94/0xe4
   kthread_worker_fn+0x118/0x328
   kthread+0x1d0/0x23c
   ret_from_fork+0x10/0x20

To prevent the crash, check for port->partner validity before
derefencing it in all the call sites.

Cc: stable@vger.kernel.org
Fixes: c97cd0b4b54e ("usb: typec: tcpm: set initial svdm version based on pd revision")
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)


base-commit: 3f12222a4bebeb13ce06ddecc1610ad32fa835dd

On Sat, Apr 27, 2024 at 1:18 PM Badhri Jagan Sridharan
<badhri@google.com> 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:
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000000000003c0
>  pc : run_state_machine+0x1bc8/0x1c08
>  lr : run_state_machine+0x1b90/0x1c08
> ..
>  Call trace:
>    run_state_machine+0x1bc8/0x1c08
>    tcpm_state_machine_work+0x94/0xe4
>    kthread_worker_fn+0x118/0x328
>    kthread+0x1d0/0x23c
>    ret_from_fork+0x10/0x20
>
> To prevent the crash, check for port->partner validity before
> derefencing it in all the call sites.
>
> Cc: stable@vger.kernel.org
> Fixes: c97cd0b4b54e ("usb: typec: tcpm: set initial svdm version based on pd revision")
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 31 +++++++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index ab6ed6111ed0..454165776797 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -4,7 +4,6 @@
>   *
>   * USB Power Delivery protocol stack.
>   */
> -
Unintentionally removed a blank line. Please ignore this version - v2.
Sent v3. Apologies !

>  #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 (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 (!port->partner)
> +               return;
> +
>         for (i = 0; i < modep->altmodes; i++) {
>                 altmode = typec_partner_register_altmode(port->partner,
>                                                 &modep->altmode_desc[i]);
> @@ -4231,7 +4234,10 @@ static int tcpm_init_vconn(struct tcpm_port *port)
>
>  static void tcpm_typec_connect(struct tcpm_port *port)
>  {
> +       struct typec_partner *partner;
> +
>         if (!port->connected) {
> +               port->connected = true;
>                 /* Make sure we don't report stale identity information */
>                 memset(&port->partner_ident, 0, sizeof(port->partner_ident));
>                 port->partner_desc.usb_pd = port->pd_capable;
> @@ -4241,9 +4247,13 @@ static void tcpm_typec_connect(struct tcpm_port *port)
>                         port->partner_desc.accessory = TYPEC_ACCESSORY_AUDIO;
>                 else
>                         port->partner_desc.accessory = TYPEC_ACCESSORY_NONE;
> -               port->partner = typec_register_partner(port->typec_port,
> -                                                      &port->partner_desc);
> -               port->connected = true;
> +               partner = typec_register_partner(port->typec_port, &port->partner_desc);
> +               if (IS_ERR(partner)) {
> +                       dev_err(port->dev, "Failed to register partner (%ld)\n", PTR_ERR(partner));
> +                       return;
> +               }
> +
> +               port->partner = partner;
>                 typec_partner_set_usb_power_delivery(port->partner, port->partner_pd);
>         }
>  }
> @@ -4323,9 +4333,11 @@ 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);
> -               port->partner = NULL;
> +               if (port->partner) {
> +                       typec_partner_set_usb_power_delivery(port->partner, NULL);
> +                       typec_unregister_partner(port->partner);
> +                       port->partner = NULL;
> +               }
>                 port->connected = false;
>         }
>  }
> @@ -4549,6 +4561,9 @@ 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 (!port->partner)
> +               return;
> +
>         switch (port->negotiated_rev) {
>         case PD_REV30:
>                 break;
>
> base-commit: 3f12222a4bebeb13ce06ddecc1610ad32fa835dd
> --
> 2.44.0.769.g3c40516874-goog
>