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

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Date:   Mon, 15 Apr 2019 13:12:25 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     syzbot <syzbot+26ec41e9f788b3eba396@...kaller.appspotmail.com>,
        andreyknvl@...gle.com, syzkaller-bugs@...glegroups.com,
        mchehab@...nel.org, corbet@....net, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: KASAN: use-after-free Read in dvb_usb_device_exit

On Fr, 2019-04-12 at 04:46 -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    9a33b369 usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan/tree/usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=1643974b200000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=23e37f59d94ddd15
> dashboard link: https://syzkaller.appspot.com/bug?extid=26ec41e9f788b3eba396
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f5efa7200000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1395a0f3200000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+26ec41e9f788b3eba396@...kaller.appspotmail.com
> 
> dvb-usb: schedule remote query interval to 150 msecs.
> dw2102: su3000_power_ctrl: 0, initialized 1
> dvb-usb: TeVii S421 PCI successfully initialized and connected.
> usb 1-1: USB disconnect, device number 2

Hi,

proposed fix. If nobody objects, I will submit it.

	Regards
		Oliver

>From d6097d205ac61745334b79639d3b8b910ae66c71 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@...e.com>
Date: Mon, 15 Apr 2019 13:06:01 +0200
Subject: [PATCH] dvb: usb: fix use after free in dvb_usb_device_exit

dvb_usb_device_exit() frees and uses teh device name in that order
Fix by storing the name in a buffer before freeing it

Signed-off-by: Oliver Neukum <oneukum@...e.com>
Reported-by: syzbot+26ec41e9f788b3eba396@...kaller.appspotmail.com
---
 drivers/media/usb/dvb-usb/dvb-usb-init.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
index 99951e02a880..2e1670cc3903 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
@@ -288,13 +288,18 @@ void dvb_usb_device_exit(struct usb_interface *intf)
 {
 	struct dvb_usb_device *d = usb_get_intfdata(intf);
 	const char *name = "generic DVB-USB module";
+	char identifier[40];
 
 	usb_set_intfdata(intf, NULL);
 	if (d != NULL && d->desc != NULL) {
 		name = d->desc->name;
+		memcpy(identifier, name, 39);
+		identifier[39] = NULL;
 		dvb_usb_exit(d);
+	} else {
+		memcpy(identifier, name, 39);
 	}
-	info("%s successfully deinitialized and disconnected.", name);
+	info("%s successfully deinitialized and disconnected.", identifier);
 
 }
 EXPORT_SYMBOL(dvb_usb_device_exit);
-- 
2.16.4