From: Kees Cook <keescook@chromium.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: syzbot <syzbot+45b2f40f0778cfa7634e@syzkaller.appspotmail.com>,
Michael Hund <mhund@ld-didactic.de>,
akpm@linux-foundation.org, andreyknvl@google.com, cai@lca.pw,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com,
tglx@linutronix.de
Subject: Re: BUG: bad usercopy in ld_usb_read
Date: Thu, 8 Aug 2019 16:06:32 -0700 [thread overview]
Message-ID: <201908081604.D1203D408@keescook> (raw)
In-Reply-To: <20190808124654.GB32144@kroah.com>
On Thu, Aug 08, 2019 at 02:46:54PM +0200, Greg KH wrote:
> On Thu, Aug 08, 2019 at 05:38:06AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: e96407b4 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=13aeaece600000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
> > dashboard link: https://syzkaller.appspot.com/bug?extid=45b2f40f0778cfa7634e
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+45b2f40f0778cfa7634e@syzkaller.appspotmail.com
> >
> > ldusb 6-1:0.124: Read buffer overflow, -131383996186150 bytes dropped
>
> That's a funny number :)
>
> Nice overflow found, I see you are now starting to fuzz the char device
> nodes of usb drivers...
>
> Michael, care to fix this up?
This looks like the length in the read-from-device buffer is unchecked:
/* actual_buffer contains actual_length + interrupt_in_buffer */
actual_buffer = (size_t *)(dev->ring_buffer + dev->ring_tail * (sizeof(size_t)+dev->interrupt_in_endpoint_size));
bytes_to_read = min(count, *actual_buffer);
if (bytes_to_read < *actual_buffer)
dev_warn(&dev->intf->dev, "Read buffer overflow, %zd bytes dropped\n",
*actual_buffer-bytes_to_read);
/* copy one interrupt_in_buffer from ring_buffer into userspace */
if (copy_to_user(buffer, actual_buffer+1, bytes_to_read)) {
retval = -EFAULT;
goto unlock_exit;
}
I assume what's stored at actual_buffer is bogus and needs validation
somewhere before it's actually used. (If not here, maybe where ever the
write into the buffer originally happens?)
--
Kees Cook
next prev parent reply other threads:[~2019-08-08 23:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 12:38 BUG: bad usercopy in ld_usb_read syzbot
2019-08-08 12:46 ` Greg KH
2019-08-08 23:06 ` Kees Cook [this message]
2019-08-09 8:55 ` Greg KH
2019-08-09 15:13 ` Alan Stern
2019-08-10 18:23 ` Kees Cook
2019-08-10 18:15 ` syzbot
2019-08-12 12:06 ` Andrey Konovalov
2019-10-18 14:39 ` Johan Hovold
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