[PATCH net 2/2] net: pse-pd: guard against freed PI data on regulator disable

[Carlo Szelinsky]

PSE PI regulators are devm-registered inside pse_controller_register(),
which runs before devres_add() arms the controller's own release in
devm_pse_controller_register(). On driver detach, devres unwinds in LIFO
order, so pse_controller_unregister() runs first and frees pcdev->pi via
pse_release_pis(); the regulators are torn down afterwards.

When regulator_unregister() flushes a pending disable, the regulator core
invokes pse_pi_disable(), which dereferences pcdev->pi[id] (directly and
via _pse_pi_disable() -> pse_pi_deallocate_pw_budget()). At that point the
PI array is already freed, so this is a use-after-free.

pse_release_pis() now clears pcdev->pi after freeing it, and
pse_pi_disable() bails out under the lock when pcdev->pi is NULL, so a
late disable from the regulator core is a no-op once the controller has
been unregistered.

Fixes: ffef61d6d273 ("net: pse-pd: Add support for budget evaluation strategies")
Signed-off-by: Carlo Szelinsky <github@xxxxxxxxxxxx>
---
 drivers/net/pse-pd/pse_core.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/pse-pd/pse_core.c b/drivers/net/pse-pd/pse_core.c
index 17f45e4b672b..9ae0df3cb5cf 100644
--- a/drivers/net/pse-pd/pse_core.c
+++ b/drivers/net/pse-pd/pse_core.c
@@ -145,6 +145,7 @@ static void pse_release_pis(struct pse_controller_dev *pcdev)
 		of_node_put(pcdev->pi[i].np);
 	}
 	kfree(pcdev->pi);
+	pcdev->pi = NULL;
 }
 
 /**
@@ -702,15 +703,21 @@ static int pse_pi_enable(struct regulator_dev *rdev)
 static int pse_pi_disable(struct regulator_dev *rdev)
 {
 	struct pse_controller_dev *pcdev = rdev_get_drvdata(rdev);
-	struct pse_pi *pi;
 	int id, ret;
 
 	id = rdev_get_id(rdev);
-	pi = &pcdev->pi[id];
 	mutex_lock(&pcdev->lock);
+	/* The controller may already be unregistered (pcdev->pi freed) by the
+	 * time the regulator core flushes a deferred disable during
+	 * regulator_unregister(). Bail out to avoid touching freed PI data.
+	 */
+	if (!pcdev->pi) {
+		mutex_unlock(&pcdev->lock);
+		return 0;
+	}
 	ret = _pse_pi_disable(pcdev, id);
 	if (!ret)
-		pi->admin_state_enabled = 0;
+		pcdev->pi[id].admin_state_enabled = 0;
 
 	mutex_unlock(&pcdev->lock);
 	return 0;
-- 
2.43.0