[PATCHv2] dvb: usb: fix use after free in dvb_usb_device_exit

[PATCHv2] dvb: usb: fix use after free in dvb_usb_device_exit

[Oliver Neukum]

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

v2: fixed style issues

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Reported-by: syzbot+26ec41e9f788b3eba396@syzkaller.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..959bbdad8f00 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] = 0;
 		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

Re: [PATCHv2] dvb: usb: fix use after free in dvb_usb_device_exit

[Mauro Carvalho Chehab]

Em Tue, 30 Apr 2019 12:43:58 +0200
Oliver Neukum <oneukum@suse.com> escreveu:

> dvb_usb_device_exit() frees and uses the device name in that order
> Fix by storing the name in a buffer before freeing it
> 
> v2: fixed style issues
> 
> Signed-off-by: Oliver Neukum <oneukum@suse.com>
> Reported-by: syzbot+26ec41e9f788b3eba396@syzkaller.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..959bbdad8f00 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";

I would change this to default_name;

> +	char identifier[40];

And use name here, instead of identifier.

IMO, this makes easier to understand the code, as it is a common practice
to call "name" for such kind of var.

>  
>  	usb_set_intfdata(intf, NULL);

>  	if (d != NULL && d->desc != NULL) {
>  		name = d->desc->name;
> +		memcpy(identifier, name, 39);
> +		identifier[39] = 0;

Please use instead (considering the rename I proposed before):

	strscpy(name, d->desc->name, sizeof(name));

>  		dvb_usb_exit(d);
> +	} else {
> +		memcpy(identifier, name, 39);

And here:

	strscpy(name, default_name, sizeof(name));

>  	}

> -	info("%s successfully deinitialized and disconnected.", name);
> +	info("%s successfully deinitialized and disconnected.", identifier);

Dropping this change.

>  
>  }
>  EXPORT_SYMBOL(dvb_usb_device_exit);



Thanks,
Mauro