linux-kernel - [RFC PATCH] usb: typec: tcpm: Ignore unsupported/unknown alternate mode requests

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Message-Id: <1564029037-22929-1-git-send-email-linux@roeck-us.net>
Date:   Wed, 24 Jul 2019 21:30:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>,
        Douglas Gilbert <dgilbert@...erlog.com>
Subject: [RFC PATCH] usb: typec: tcpm: Ignore unsupported/unknown alternate mode requests

TCPM may receive PD messages associated with unknown or unsupported
alternate modes. If that happens, calls to typec_match_altmode()
will return NULL. The tcpm code does not currently take this into
account. This results in crashes.

Unable to handle kernel NULL pointer dereference at virtual address 000001f0
pgd = 41dad9a1
[000001f0] *pgd=00000000
Internal error: Oops: 5 [#1] THUMB2
Modules linked in: tcpci tcpm
CPU: 0 PID: 2338 Comm: kworker/u2:0 Not tainted 5.1.18-sama5-armv7-r2 #6
Hardware name: Atmel SAMA5
Workqueue: 2-0050 tcpm_pd_rx_handler [tcpm]
PC is at typec_altmode_attention+0x0/0x14
LR is at tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm]
...
[<c03fbee8>] (typec_altmode_attention) from [<bf8030fb>]
				(tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm])
[<bf8030fb>] (tcpm_pd_rx_handler [tcpm]) from [<c012082b>]
				(process_one_work+0x123/0x2a8)
[<c012082b>] (process_one_work) from [<c0120a6d>]
				(worker_thread+0xbd/0x3b0)
[<c0120a6d>] (worker_thread) from [<c012431f>] (kthread+0xcf/0xf4)
[<c012431f>] (kthread) from [<c01010f9>] (ret_from_fork+0x11/0x38)

Ignore PD messages if the asociated alternate mode is not supported.

Reported-by: Douglas Gilbert <dgilbert@...erlog.com>
Cc: Douglas Gilbert <dgilbert@...erlog.com>
Fixes: e9576fe8e605c ("usb: typec: tcpm: Support for Alternate Modes")
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
Taking a stab at the problem. I don't really know if this is the correct
fix, or even if my understanding of the problem is correct, thus marking
the patch as RFC.

 drivers/usb/typec/tcpm/tcpm.c | 38 ++++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 77f71f602f73..1df2844469aa 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -1096,7 +1096,8 @@ static int tcpm_pd_svdm(struct tcpm_port *port, const __le32 *payload, int cnt,
 			break;
 		case CMD_ATTENTION:
 			/* Attention command does not have response */
-			typec_altmode_attention(adev, p[1]);
+			if (adev)
+				typec_altmode_attention(adev, p[1]);
 			return 0;
 		default:
 			break;
@@ -1148,20 +1149,26 @@ static int tcpm_pd_svdm(struct tcpm_port *port, const __le32 *payload, int cnt,
 			}
 			break;
 		case CMD_ENTER_MODE:
-			typec_altmode_update_active(pdev, true);
-
-			if (typec_altmode_vdm(adev, p[0], &p[1], cnt)) {
-				response[0] = VDO(adev->svid, 1, CMD_EXIT_MODE);
-				response[0] |= VDO_OPOS(adev->mode);
-				return 1;
+			if (adev && pdev) {
+				typec_altmode_update_active(pdev, true);
+
+				if (typec_altmode_vdm(adev, p[0], &p[1], cnt)) {
+					response[0] = VDO(adev->svid, 1,
+							  CMD_EXIT_MODE);
+					response[0] |= VDO_OPOS(adev->mode);
+					return 1;
+				}
 			}
 			return 0;
 		case CMD_EXIT_MODE:
-			typec_altmode_update_active(pdev, false);
+			if (adev && pdev) {
+				typec_altmode_update_active(pdev, false);
 
-			/* Back to USB Operation */
-			WARN_ON(typec_altmode_notify(adev, TYPEC_STATE_USB,
-						     NULL));
+				/* Back to USB Operation */
+				WARN_ON(typec_altmode_notify(adev,
+							     TYPEC_STATE_USB,
+							     NULL));
+			}
 			break;
 		default:
 			break;
@@ -1171,8 +1178,10 @@ static int tcpm_pd_svdm(struct tcpm_port *port, const __le32 *payload, int cnt,
 		switch (cmd) {
 		case CMD_ENTER_MODE:
 			/* Back to USB Operation */
-			WARN_ON(typec_altmode_notify(adev, TYPEC_STATE_USB,
-						     NULL));
+			if (adev)
+				WARN_ON(typec_altmode_notify(adev,
+							     TYPEC_STATE_USB,
+							     NULL));
 			break;
 		default:
 			break;
@@ -1183,7 +1192,8 @@ static int tcpm_pd_svdm(struct tcpm_port *port, const __le32 *payload, int cnt,
 	}
 
 	/* Informing the alternate mode drivers about everything */
-	typec_altmode_vdm(adev, p[0], &p[1], cnt);
+	if (adev)
+		typec_altmode_vdm(adev, p[0], &p[1], cnt);
 
 	return rlen;
 }
-- 
2.7.4