FAILED: patch "[PATCH] staging: rtl8712: fix use-after-free in rtl8712_dl_fw" failed to apply to 4.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c052cc1a069c3e575619cf64ec427eb41176ca70 Mon Sep 17 00:00:00 2001
From: Pavel Skripkin <paskripkin@gmail.com>
Date: Wed, 20 Oct 2021 00:17:18 +0300
Subject: [PATCH] staging: rtl8712: fix use-after-free in rtl8712_dl_fw

Syzbot reported use-after-free in rtl8712_dl_fw(). The problem was in
race condition between r871xu_dev_remove() ->ndo_open() callback.

It's easy to see from crash log, that driver accesses released firmware
in ->ndo_open() callback. It may happen, since driver was releasing
firmware _before_ unregistering netdev. Fix it by moving
unregister_netdev() before cleaning up resources.

Call Trace:
...
 rtl871x_open_fw drivers/staging/rtl8712/hal_init.c:83 [inline]
 rtl8712_dl_fw+0xd95/0xe10 drivers/staging/rtl8712/hal_init.c:170
 rtl8712_hal_init drivers/staging/rtl8712/hal_init.c:330 [inline]
 rtl871x_hal_init+0xae/0x180 drivers/staging/rtl8712/hal_init.c:394
 netdev_open+0xe6/0x6c0 drivers/staging/rtl8712/os_intfs.c:380
 __dev_open+0x2bc/0x4d0 net/core/dev.c:1484

Freed by task 1306:
...
 release_firmware+0x1b/0x30 drivers/base/firmware_loader/main.c:1053
 r871xu_dev_remove+0xcc/0x2c0 drivers/staging/rtl8712/usb_intf.c:599
 usb_unbind_interface+0x1d8/0x8d0 drivers/usb/core/driver.c:458

Fixes: 8c213fa59199 ("staging: r8712u: Use asynchronous firmware loading")
Cc: stable <stable@vger.kernel.org>
Reported-and-tested-by: syzbot+c55162be492189fb4f51@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20211019211718.26354-1-paskripkin@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/rtl8712/usb_intf.c b/drivers/staging/rtl8712/usb_intf.c
index 17e705411e64..ee4c61f85a07 100644
--- a/drivers/staging/rtl8712/usb_intf.c
+++ b/drivers/staging/rtl8712/usb_intf.c
@@ -595,12 +595,12 @@ static void r871xu_dev_remove(struct usb_interface *pusb_intf)
 
 	/* never exit with a firmware callback pending */
 	wait_for_completion(&padapter->rtl8712_fw_ready);
+	if (pnetdev->reg_state != NETREG_UNINITIALIZED)
+		unregister_netdev(pnetdev); /* will call netdev_close() */
 	usb_set_intfdata(pusb_intf, NULL);
 	release_firmware(padapter->fw);
 	if (drvpriv.drv_registered)
 		padapter->surprise_removed = true;
-	if (pnetdev->reg_state != NETREG_UNINITIALIZED)
-		unregister_netdev(pnetdev); /* will call netdev_close() */
 	r8712_flush_rwctrl_works(padapter);
 	r8712_flush_led_works(padapter);
 	udelay(1);