[PATCH v14 1/4] phy: core: Fix use-after-free in phy_get paths

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

Sashiko asked during a patch review if the existing usage pattern had a
race condition; specifically in of_phy_get() if it was possible between
returning from _of_phy_get() and running try_module_get() that a module
might be unbound leading to use-after-free.

Looking at the code this appears to be so, there is no linkage between the
phy and module under a synchronisation primitive.

Using the phy_provider_mutex in phy_get() will ensure there is a link between
the returned phy pointer and the module_get() bumping the module reference
count.

Amend phy_get(), of_phy_get() and devm_of_phy_get_by_index() to fix the
same usage pattern.

phy_provider_unregister() must take the phy_provider_mutex so amending
phy_get()/of_phy_get() to take that same mutex guarantees there is no
use-after-free.

Fixes: ff764963479a1 ("drivers: phy: add generic PHY framework")
Cc: stable@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
---
 drivers/phy/phy-core.c | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
index 21aaf2f76e53e..cd9ace125567a 100644
--- a/drivers/phy/phy-core.c
+++ b/drivers/phy/phy-core.c
@@ -124,13 +124,11 @@ static struct phy *phy_find(struct device *dev, const char *con_id)
 	const char *dev_id = dev_name(dev);
 	struct phy_lookup *p, *pl = NULL;
 
-	mutex_lock(&phy_provider_mutex);
 	list_for_each_entry(p, &phys, node)
 		if (!strcmp(p->dev_id, dev_id) && !strcmp(p->con_id, con_id)) {
 			pl = p;
 			break;
 		}
-	mutex_unlock(&phy_provider_mutex);
 
 	return pl ? pl->phy : ERR_PTR(-ENODEV);
 }
@@ -635,11 +633,10 @@ static struct phy *_of_phy_get(struct device_node *np, int index)
 		goto out_put_node;
 	}
 
-	mutex_lock(&phy_provider_mutex);
 	phy_provider = of_phy_provider_lookup(args.np);
 	if (IS_ERR(phy_provider) || !try_module_get(phy_provider->owner)) {
 		phy = ERR_PTR(-EPROBE_DEFER);
-		goto out_unlock;
+		goto out_put_node;
 	}
 
 	if (!of_device_is_available(args.np)) {
@@ -653,8 +650,6 @@ static struct phy *_of_phy_get(struct device_node *np, int index)
 out_put_module:
 	module_put(phy_provider->owner);
 
-out_unlock:
-	mutex_unlock(&phy_provider_mutex);
 out_put_node:
 	of_node_put(args.np);
 
@@ -678,15 +673,21 @@ struct phy *of_phy_get(struct device_node *np, const char *con_id)
 	if (con_id)
 		index = of_property_match_string(np, "phy-names", con_id);
 
+	mutex_lock(&phy_provider_mutex);
+
 	phy = _of_phy_get(np, index);
 	if (IS_ERR(phy))
-		return phy;
+		goto out_unlock;
 
-	if (!try_module_get(phy->ops->owner))
-		return ERR_PTR(-EPROBE_DEFER);
+	if (!try_module_get(phy->ops->owner)) {
+		phy = ERR_PTR(-EPROBE_DEFER);
+		goto out_unlock;
+	}
 
 	get_device(&phy->dev);
 
+out_unlock:
+	mutex_unlock(&phy_provider_mutex);
 	return phy;
 }
 EXPORT_SYMBOL_GPL(of_phy_get);
@@ -786,6 +787,7 @@ struct phy *phy_get(struct device *dev, const char *string)
 	struct phy *phy;
 	struct device_link *link;
 
+	mutex_lock(&phy_provider_mutex);
 	if (dev->of_node) {
 		if (string)
 			index = of_property_match_string(dev->of_node, "phy-names",
@@ -796,15 +798,18 @@ struct phy *phy_get(struct device *dev, const char *string)
 	} else {
 		if (string == NULL) {
 			dev_WARN(dev, "missing string\n");
-			return ERR_PTR(-EINVAL);
+			phy = ERR_PTR(-EINVAL);
+			goto out_unlock;
 		}
 		phy = phy_find(dev, string);
 	}
 	if (IS_ERR(phy))
-		return phy;
+		goto out_unlock;
 
-	if (!try_module_get(phy->ops->owner))
-		return ERR_PTR(-EPROBE_DEFER);
+	if (!try_module_get(phy->ops->owner)) {
+		phy = ERR_PTR(-EPROBE_DEFER);
+		goto out_unlock;
+	}
 
 	get_device(&phy->dev);
 
@@ -813,6 +818,8 @@ struct phy *phy_get(struct device *dev, const char *string)
 		dev_dbg(dev, "failed to create device link to %s\n",
 			dev_name(phy->dev.parent));
 
+out_unlock:
+	mutex_unlock(&phy_provider_mutex);
 	return phy;
 }
 EXPORT_SYMBOL_GPL(phy_get);
@@ -961,15 +968,17 @@ struct phy *devm_of_phy_get_by_index(struct device *dev, struct device_node *np,
 	if (!ptr)
 		return ERR_PTR(-ENOMEM);
 
+	mutex_lock(&phy_provider_mutex);
 	phy = _of_phy_get(np, index);
 	if (IS_ERR(phy)) {
 		devres_free(ptr);
-		return phy;
+		goto out_unlock;
 	}
 
 	if (!try_module_get(phy->ops->owner)) {
 		devres_free(ptr);
-		return ERR_PTR(-EPROBE_DEFER);
+		phy = ERR_PTR(-EPROBE_DEFER);
+		goto out_unlock;
 	}
 
 	get_device(&phy->dev);
@@ -982,6 +991,8 @@ struct phy *devm_of_phy_get_by_index(struct device *dev, struct device_node *np,
 		dev_dbg(dev, "failed to create device link to %s\n",
 			dev_name(phy->dev.parent));
 
+out_unlock:
+	mutex_unlock(&phy_provider_mutex);
 	return phy;
 }
 EXPORT_SYMBOL_GPL(devm_of_phy_get_by_index);

-- 
2.55.0