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usb: typec: altmodes/displayport: add null pointer check for sysfs nodes

PATCH In review RD Babiera 2 participants 3 messages Jan 30, 2024 – Feb 26, 2024

Subsystems (4)
Stable branch USB USB Type-C class USB Type-C bus for alternate modes
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RD Babiera

author
#0 lore raw

PATCH 1/1 usb: typec: altmodes/displayport: add null pointer check for sysfs nodes

The DisplayPort driver's sysfs nodes may be present to the userspace before typec_altmode_set_drvdata() completes in dp_altmode_probe. This means that a sysfs read can trigger a NULL pointer error by deferencing dp->hpd in hpd_show or dp->lock in pin_assignment_show, as dev_get_drvdata() returns NULL in those cases.

Verify dp drvdata is present in sysfs reads and writes before proceeding.

Fixes 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc [email protected]
Signed-off-by RD Babiera <[email protected]>
---
 drivers/usb/typec/altmodes/displayport.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
drivers/usb/typec/altmodes/displayport.c +15 -0
index 5a80776c7255..0423326219d8 100644
@@ -518,6 +518,9 @@ configuration_store(struct device *dev, struct device_attribute *attr,
 	int con;
 	int ret = 0;
 
+	if (!dp)
+		return -ENODEV;
+
 	con = sysfs_match_string(configurations, buf);
 	if (con < 0)
 		return con;

@@ -563,6 +566,9 @@ static ssize_t configuration_show(struct device *dev,
 	u8 cur;
 	int i;
 
+	if (!dp)
+		return -ENODEV;
+
 	mutex_lock(&dp->lock);
 
 	cap = DP_CAP_CAPABILITY(dp->alt->vdo);

@@ -615,6 +621,9 @@ pin_assignment_store(struct device *dev, struct device_attribute *attr,
 	u32 conf;
 	int ret;
 
+	if (!dp)
+		return -ENODEV;
+
 	ret = sysfs_match_string(pin_assignments, buf);
 	if (ret < 0)
 		return ret;

@@ -666,6 +675,9 @@ static ssize_t pin_assignment_show(struct device *dev,
 	u8 cur;
 	int i;
 
+	if (!dp)
+		return -ENODEV;
+
 	mutex_lock(&dp->lock);
 
 	cur = get_count_order(DP_CONF_GET_PIN_ASSIGN(dp->data.conf));

@@ -698,6 +710,9 @@ static ssize_t hpd_show(struct device *dev, struct device_attribute *attr, char
 {
 	struct dp_altmode *dp = dev_get_drvdata(dev);
 
+	if (!dp)
+		return -ENODEV;
+
 	return sysfs_emit(buf, "%d\n", dp->hpd);
 }
 static DEVICE_ATTR_RO(hpd);

base-commit: f1a27f081c1fa1eeebf38406e45f29636114470f

Signature · 1 line
2.43.0.429.g432eaa2c6b-goog
maintainer
#1 lore raw
Quoted 7 lines · RD Babiera

The DisplayPort driver's sysfs nodes may be present to the userspace before typec_altmode_set_drvdata() completes in dp_altmode_probe. This means that a sysfs read can trigger a NULL pointer error by deferencing dp->hpd in hpd_show or dp->lock in pin_assignment_show, as dev_get_drvdata() returns NULL in those cases.

Verify dp drvdata is present in sysfs reads and writes before proceeding.

Why not populate the sysfs nodes after the assigment happens? That's the normal way to do this, otherwise your change looks odd because:

Quoted 13 lines
Fixes 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc [email protected]
Signed-off-by RD Babiera <[email protected]>
---
 drivers/usb/typec/altmodes/displayport.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
drivers/usb/typec/altmodes/displayport.c +0 -0
index 5a80776c7255..0423326219d8 100644

drivers/usb/typec/altmodes/displayport.c configuration_store(struct device *dev, struct device_attribute *attr, · line 524

Quoted 7 lines
drivers/usb/typec/altmodes/displayport.c +3 -0
@@ -518,6 +518,9 @@ configuration_store(struct device *dev, struct device_attribute *attr,
 	int con;
 	int ret = 0;
 
+	if (!dp)
+		return -ENODEV;
+
 	con = sysfs_match_string(configurations, buf);

there's nothing keeping dp from being an invalid pointer right after you check it. Really that might not happen, but it's hard to tell that here.

thanks,

greg k-h

author
#2 lore raw

Sorry for the delay,

Quoted 2 lines · Greg KH

Why not populate the sysfs nodes after the assigment happens? That's the normal way to do this, otherwise your change looks odd because:

That works a lot better. I must've psyched myself out of touching the current probe sequence and ended up overcomplicating it, sorry about that.

Thanks for the guidance,
RD