Re: [PATCH 5.4 17/78] HID: Fix slab-out-of-bounds read in hid_field_extract (Broken!)

Enderborg, Peter
2020-02-05T09:49:36Z

On 2/5/20 10:32 AM, Greg Kroah-Hartman wrote:
> On Wed, Feb 05, 2020 at 08:12:27AM +0100, peter enderborg wrote:
>> On 1/14/20 11:00 AM, Greg Kroah-Hartman wrote:
>>> From: Alan Stern <stern@rowland.harvard.edu>
>>>
>>> commit 8ec321e96e056de84022c032ffea253431a83c3c upstream.
>>>
>>> The syzbot fuzzer found a slab-out-of-bounds bug in the HID report
>>> handler. The bug was caused by a report descriptor which included a
>>> field with size 12 bits and count 4899, for a total size of 7349
>>> bytes.
>>>
>>> The usbhid driver uses at most a single-page 4-KB buffer for reports.
>>> In the test there wasn't any problem about overflowing the buffer,
>>> since only one byte was received from the device. Rather, the bug
>>> occurred when the HID core tried to extract the data from the report
>>> fields, which caused it to try reading data beyond the end of the
>>> allocated buffer.
>>>
>>> This patch fixes the problem by rejecting any report whose total
>>> length exceeds the HID_MAX_BUFFER_SIZE limit (minus one byte to allow
>>> for a possible report index). In theory a device could have a report
>>> longer than that, but if there was such a thing we wouldn't handle it
>>> correctly anyway.
>>>
>>> Reported-and-tested-by: syzbot+09ef48aa58261464b621@syzkaller.appspotmail.com
>>> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
>>> CC: <stable@vger.kernel.org>
>>> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>
>>> ---
>>> drivers/hid/hid-core.c | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> --- a/drivers/hid/hid-core.c
>>> +++ b/drivers/hid/hid-core.c
>>> @@ -288,6 +288,12 @@ static int hid_add_field(struct hid_pars
>>> offset = report->size;
>>> report->size += parser->global.report_size * parser->global.report_count;
>>>
>>> + /* Total size check: Allow for possible report index byte */
>>> + if (report->size > (HID_MAX_BUFFER_SIZE - 1) << 3) {
>>> + hid_err(parser->device, "report is too long\n");
>>> + return -1;
>>> + }
>>> +
>>> if (!parser->local.usage_index) /* Ignore padding fields */
>>> return 0;
>>>
>>>
>>>
>>>
>> This patch breaks Elgato StreamDeck.
> Does that mean the device is broken with a too-large of a report?

Yes.

> Is it broken in Linus's tree? If so, can you work with the HID
> developers to fix it there so we can backport the fix to all stable
> trees?

I cant see that there are any other fixes upon this so I dont think so. I can try.

Jiri is in the loop. I guess he is the "HID developers" ?

>
> thanks,
>
> greg k-h