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SubjectRe: KASAN: use-after-free Read in dvb_usb_device_exit
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On 4/15/19 1:12 PM, Oliver Neukum wrote:
> 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@syzkaller.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@suse.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@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..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);

Why not just move this to after the info()? You'll need to repeat the
'if' in that case, but that way there is no need to memcpy anything.

Regards,

Hans

> + } 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);
>

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