[PATCH 3/3] power: supply: mt6360_charger: drain chrdet_work before the power supply is freed

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

mt6360_charger_probe() registers the chrdet_work cancellation via
devm_work_autocancel() *before* devm_power_supply_register(), so devres
(which unwinds in reverse) frees the power supply device first and only
then cancels the work:

	devm_work_autocancel(..., &mci->chrdet_work, ...);   /* registered 1st */
	...
	mci->psy = devm_power_supply_register(...);          /* registered 2nd */
	...
	schedule_work(&mci->chrdet_work);

The work handler mt6360_chrdet_work() runs mt6360_handle_chrdet_ext_evt(),
which calls power_supply_changed(mci->psy). chrdet_work is scheduled at
the end of probe, so on an unbind that races that work, devres tears down
in reverse order: devm_power_supply_register()'s release frees the power
supply device before the devm_work_autocancel action drains chrdet_work,
and the work then dereferences the freed mci->psy -> use-after-free.

Register the work cancellation after devm_power_supply_register() (and
after the other devm resources), so reverse-order devres cleanup drains
chrdet_work while mci->psy is still valid. chrdet_work is only scheduled
later in probe, so moving the devm_work_autocancel() (which also
initialises the work) down is safe.

Found by code review; not runtime-reproduced (requires MT6360 PMIC
hardware and a charger-detect event racing device unbind).

[USER: add a Fixes: tag. SHA not verifiable in this graft-at-7.3 worktree.
 Blame the devm_work_autocancel() introduction in mt6360_charger.c on a
 full-history tree and confirm the 12-char SHA + subject before send.]
Fixes: 0402e8ebb8b8 ("power: supply: mt6360_charger: add MT6360 charger support")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
 drivers/power/supply/mt6360_charger.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/power/supply/mt6360_charger.c b/drivers/power/supply/mt6360_charger.c
index b4d4623..e382db4 100644
--- a/drivers/power/supply/mt6360_charger.c
+++ b/drivers/power/supply/mt6360_charger.c
@@ -790,9 +790,6 @@ static int mt6360_charger_probe(struct platform_device *pdev)
 	mci->vinovp = 6500000;
 	mutex_init(&mci->chgdet_lock);
 	platform_set_drvdata(pdev, mci);
-	ret = devm_work_autocancel(&pdev->dev, &mci->chrdet_work, mt6360_chrdet_work);
-	if (ret)
-		return dev_err_probe(&pdev->dev, ret, "Failed to set delayed work\n");
 
 	ret = device_property_read_u32(&pdev->dev, "richtek,vinovp-microvolt", &mci->vinovp);
 	if (ret)
@@ -828,6 +825,16 @@ static int mt6360_charger_probe(struct platform_device *pdev)
 	if (IS_ERR(mci->otg_rdev))
 		return PTR_ERR(mci->otg_rdev);
 
+	/*
+	 * Register the work cancellation only after the power supply is
+	 * registered.  devres unwinds in reverse, so this guarantees the
+	 * work (which calls power_supply_changed(mci->psy)) is drained
+	 * before the power supply device is freed on unbind.
+	 */
+	ret = devm_work_autocancel(&pdev->dev, &mci->chrdet_work, mt6360_chrdet_work);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "Failed to set delayed work\n");
+
 	schedule_work(&mci->chrdet_work);
 
 	return 0;
-- 
2.43.0