Subject: Re: KASAN: use-after-free Read in p54u_load_firmware_cb

From: Oliver Neukum <[email-masked]>
Date: Mon, 13 May 2019 15:28:30 +0200

On Mo, 2019-05-13 at 03:23 -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    43151d6c usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=16b64110a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4183eeef650d1234
> dashboard link: https://syzkaller.appspot.com/bug?extid=200d4bb11b23d929335f
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1634c900a00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email-masked]
> 
> usb 1-1: config 0 descriptor??
> usb 1-1: reset high-speed USB device number 2 using dummy_hcd
> usb 1-1: device descriptor read/64, error -71
> usb 1-1: Using ep0 maxpacket: 8
> usb 1-1: Loading firmware file isl3887usb
> usb 1-1: Direct firmware load for isl3887usb failed with error -2
> usb 1-1: Firmware not found.
> ==================================================================
> BUG: KASAN: use-after-free in p54u_load_firmware_cb.cold+0x97/0x13a  
> drivers/net/wireless/intersil/p54/p54usb.c:936
> Read of size 8 at addr ffff88809803f588 by task kworker/1:0/17

Hi,

it looks to me as if refcounting is broken.
You should have a usb_put_dev() in p54u_load_firmware_cb() or in
p54u_disconnect(), but not both.

	Regards
		Oliver