[PATCH v2] usb: gadget: lpc32xx_udc: drain the pullup work on removal

[Hyunjung Ko]

isp1301_pullup_enable() schedules udc->pullup_job to perform the slow
isp1301 i2c pull-up access from process context. The work handler
(pullup_work) dereferences udc and touches the isp1301 i2c client.

udc is allocated with devm_kmemdup(), so devres frees it after
lpc32xx_udc_remove() returns. remove() calls pullup(udc, 0) -- which
queues pullup_job to clear the D+ pull-up -- but never drains it, so the
work can run after udc has been freed (and the isp1301 client put),
dereferencing freed memory -- a use-after-free.

Flush pullup_job in lpc32xx_udc_remove() after the final pullup(udc, 0).
flush_work() (rather than cancel_work_sync()) lets the queued pull-up
disable actually complete before the udc and its isp1301 client are
released, so the transceiver is left with D+ deasserted.

Found by static analysis; not runtime-reproduced (needs LPC32xx USB
gadget hardware with the isp1301 transceiver).

Fixes: 24a28e428351 ("USB: gadget driver for LPC32xx")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hyunjung Ko <hj351016@xxxxxxxxx>
---
v2: flush_work() instead of cancel_work_sync(), so the pull-up disable
    queued by pullup(udc, 0) completes rather than being dropped
    (OTG1_DP_PULLUP would otherwise stay asserted after unbind) -- per
    Sashiko review of v1.

 drivers/usb/gadget/udc/lpc32xx_udc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/usb/gadget/udc/lpc32xx_udc.c b/drivers/usb/gadget/udc/lpc32xx_udc.c
index 94355d3d930f..b98faf5b71e5 100644
--- a/drivers/usb/gadget/udc/lpc32xx_udc.c
+++ b/drivers/usb/gadget/udc/lpc32xx_udc.c
@@ -3187,6 +3187,13 @@ static void lpc32xx_udc_remove(struct platform_device *pdev)
 	udc_disable(udc);
 	pullup(udc, 0);

+	/*
+	 * pullup(udc, 0) queues pullup_job to clear the D+ pull-up over i2c;
+	 * flush it so that disable completes and no work can run after the
+	 * devm-allocated udc (and its isp1301 i2c client) are released.
+	 */
+	flush_work(&udc->pullup_job);
+
 	device_init_wakeup(&pdev->dev, 0);
 	remove_debug_file(udc);

--
2.43.0