linux-kernel - Re: KASAN: use-after-free Read in cpia2_usb

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Date:   Wed, 03 Jul 2019 09:42:09 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     syzbot <syzbot+0c90fc937c84f97d0aa6@...kaller.appspotmail.com>,
        keescook@...omium.org, andreyknvl@...gle.com,
        syzkaller-bugs@...glegroups.com, mchehab@...nel.org,
        tglx@...utronix.de, sakari.ailus@...ux.intel.com,
        kstewart@...uxfoundation.org, allison@...utok.net,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-usb@...r.kernel.org, hverkuil-cisco@...all.nl
Subject: Re: KASAN: use-after-free Read in cpia2_usb_disconnect

Am Dienstag, den 02.07.2019, 18:01 -0700 schrieb syzbot:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    7829a896 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=11e19043a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f6d4561982f71f63
> dashboard link: https://syzkaller.appspot.com/bug?extid=0c90fc937c84f97d0aa6
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=147d42eda00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=104c268ba00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0c90fc937c84f97d0aa6@...kaller.appspotmail.com
> 
> cpia2: Message: count = 1, register[0] = 0x0
> cpia2: Unexpected error: -19
> ==================================================================
> BUG: KASAN: use-after-free in cpia2_usb_disconnect+0x1a4/0x1c0  
> drivers/media/usb/cpia2/cpia2_usb.c:898
> Read of size 8 at addr ffff8881cf6c4e50 by task kworker/1:1/22

Please try this:

>From a0a73298fc23acb95e7b6487e960be707563eb34 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@...e.com>
Date: Wed, 8 May 2019 12:36:40 +0200
Subject: [PATCH] cpia2_usb: first wake up, then free in disconnect

Kasan reported a use after free in cpia2_usb_disconnect()
It first freed everything and then woke up those waiting.
The reverse order is correct.

Signed-off-by: Oliver Neukum <oneukum@...e.com>
Reported-by: syzbot+0c90fc937c84f97d0aa6@...kaller.appspotmail.com
Fixes: 6c493f8b28c67 ("[media] cpia2: major overhaul to get it in a working state again")
---
 drivers/media/usb/cpia2/cpia2_usb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/cpia2/cpia2_usb.c b/drivers/media/usb/cpia2/cpia2_usb.c
index e5d8dee38fe4..44bd7e5ad3eb 100644
--- a/drivers/media/usb/cpia2/cpia2_usb.c
+++ b/drivers/media/usb/cpia2/cpia2_usb.c
@@ -902,7 +902,6 @@ static void cpia2_usb_disconnect(struct usb_interface *intf)
 	cpia2_unregister_camera(cam);
 	v4l2_device_disconnect(&cam->v4l2_dev);
 	mutex_unlock(&cam->v4l2_lock);
-	v4l2_device_put(&cam->v4l2_dev);
 
 	if(cam->buffers) {
 		DBG("Wakeup waiting processes\n");
@@ -911,6 +910,8 @@ static void cpia2_usb_disconnect(struct usb_interface *intf)
 		wake_up_interruptible(&cam->wq_stream);
 	}
 
+	v4l2_device_put(&cam->v4l2_dev);
+
 	LOG("CPiA2 camera disconnected.\n");
 }
 
-- 
2.16.4