[PATCH 03/24] media: netup_unidvb: fix use-after-free bug caused by del_timer()

From: Mauro Carvalho Chehab
Date: Sat May 13 2023 - 13:58:06 EST

From: Duoming Zhou <duoming@xxxxxxxxxx>

When Universal DVB card is detaching, netup_unidvb_dma_fini()
uses del_timer() to stop dma->timeout timer. But when timer
handler netup_unidvb_dma_timeout() is running, del_timer()
could not stop it. As a result, the use-after-free bug could
happen. The process is shown below:

(cleanup routine) | (timer routine)
| mod_timer(&dev->tx_sim_timer, ..)
netup_unidvb_finidev() | (wait a time)
netup_unidvb_dma_fini() | netup_unidvb_dma_timeout()
del_timer(&dma->timeout); |
| ndev->pci_dev->dev //USE

Fix by changing del_timer() to del_timer_sync().

Link: https://lore.kernel.org/linux-media/20230308125514.4208-1-duoming@xxxxxxxxxx
Fixes: 52b1eaf4c59a ("[media] netup_unidvb: NetUP Universal DVB-S/S2/T/T2/C PCI-E card driver")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
drivers/media/pci/netup_unidvb/netup_unidvb_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/pci/netup_unidvb/netup_unidvb_core.c b/drivers/media/pci/netup_unidvb/netup_unidvb_core.c
index 8287851b5ffd..aaa1d2dedebd 100644
--- a/drivers/media/pci/netup_unidvb/netup_unidvb_core.c
+++ b/drivers/media/pci/netup_unidvb/netup_unidvb_core.c
@@ -697,7 +697,7 @@ static void netup_unidvb_dma_fini(struct netup_unidvb_dev *ndev, int num)
netup_unidvb_dma_enable(dma, 0);
- del_timer(&dma->timeout);
+ del_timer_sync(&dma->timeout);

static int netup_unidvb_dma_setup(struct netup_unidvb_dev *ndev)