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Date: Tue, 26 Mar 2024 23:19:09 +0800
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Message-ID: <20240326151909.440275-1-kyletso@google.com>
Subject: [PATCH v2] usb: typec: tcpm: Correct the PDO counting in pd_set
From: Kyle Tso <kyletso@google.com>
To: linux@roeck-us.net, heikki.krogerus@linux.intel.com, 
	gregkh@linuxfoundation.org
Cc: badhri@google.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, 
	Kyle Tso <kyletso@google.com>, stable@vger.kernel.org
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Off-by-one errors happen because nr_snk_pdo and nr_src_pdo are
incorrectly added one. The index of the loop is equal to the number of
PDOs to be updated when leaving the loop and it doesn't need to be added
one.

When doing the power negotiation, TCPM relies on the "nr_snk_pdo" as
the size of the local sink PDO array to match the Source capabilities
of the partner port. If the off-by-one overflow occurs, a wrong RDO
might be sent and unexpected power transfer might happen such as over
voltage or over current (than expected).

"nr_src_pdo" is used to set the Rp level when the port is in Source
role. It is also the array size of the local Source capabilities when
filling up the buffer which will be sent as the Source PDOs (such as
in Power Negotiation). If the off-by-one overflow occurs, a wrong Rp
level might be set and wrong Source PDOs will be sent to the partner
port. This could potentially cause over current or port resets.

Fixes: cd099cde4ed2 ("usb: typec: tcpm: Support multiple capabilities")
Cc: stable@vger.kernel.org
Signed-off-by: Kyle Tso <kyletso@google.com>
---
v1 -> v2:
- update the commit message (adding the problems this patch solves)

 drivers/usb/typec/tcpm/tcpm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index ae2b6c94482d..2464710ea0c8 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -6855,14 +6855,14 @@ static int tcpm_pd_set(struct typec_port *p, struct usb_power_delivery *pd)
 	if (data->sink_desc.pdo[0]) {
 		for (i = 0; i < PDO_MAX_OBJECTS && data->sink_desc.pdo[i]; i++)
 			port->snk_pdo[i] = data->sink_desc.pdo[i];
-		port->nr_snk_pdo = i + 1;
+		port->nr_snk_pdo = i;
 		port->operating_snk_mw = data->operating_snk_mw;
 	}
 
 	if (data->source_desc.pdo[0]) {
 		for (i = 0; i < PDO_MAX_OBJECTS && data->source_desc.pdo[i]; i++)
 			port->snk_pdo[i] = data->source_desc.pdo[i];
-		port->nr_src_pdo = i + 1;
+		port->nr_src_pdo = i;
 	}
 
 	switch (port->state) {
-- 
2.44.0.396.g6e790dbe36-goog