From: Peilin Ye <yepeilin.cs@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Jiri Kosina <jikos@kernel.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
syzkaller-bugs@googlegroups.com,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-usb@vger.kernel.org, linux-input@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH v1] usbhid: Fix slab-out-of-bounds write in hiddev_ioctl_usage()
Date: Mon, 20 Jul 2020 15:05:08 -0400 [thread overview]
Message-ID: <20200720190508.GA1946@PWN> (raw)
In-Reply-To: <20200720121257.GJ2571@kadam>
On Mon, Jul 20, 2020 at 03:12:57PM +0300, Dan Carpenter wrote:
> So another option would be to just add HIDIOCGUSAGE and HIDIOCSUSAGE to
> the earlier check. That risks breaking userspace. Another option is to
> just add a check like you did earlier to the HIDIOCGUSAGE case.
> Probably just do option #2 and resend.
Sure, I will just add the same check to the HIDIOCGUSAGE case for the
time being. Thank you for the detailed explanation.
Here's what I found after digging a bit further though:
hid_parser_main() calls different functions in order to process
different type of items:
drivers/hid/hid-core.c:1193:
static int (*dispatch_type[])(struct hid_parser *parser,
struct hid_item *item) = {
hid_parser_main,
hid_parser_global,
hid_parser_local,
hid_parser_reserved
};
In this case, hid_parser_main() calls hid_add_field(), which in turn
calls hid_register_field(), which allocates the `field` object as you
mentioned:
drivers/hid/hid-core.c:102:
field = kzalloc((sizeof(struct hid_field) +
usages * sizeof(struct hid_usage) +
values * sizeof(unsigned)), GFP_KERNEL);
Here, `values` equals to `global.report_count`. See how it is being
called:
drivers/hid/hid-core.c:303:
field = hid_register_field(report, usages, parser->global.report_count);
In hid_parser_main(), `global.report_count` can be set by calling
hid_parser_global().
However, the syzkaller reproducer made hid_parser_main() to call
hid_parser_global() __before__ `global.report_count` is properly set. It's
zero. So hid_register_field() allocated `field` with `values` equals to
zero - No room for value[] at all. I believe this caused the bug.
Apparently hid_parser_main() doesn't care about which item (main, local,
global and reserved) gets processed first. I am new to this code and I
don't know whether this is by design, but this arbitrarity is
apparently causing some issues.
As another example, in hid_add_field():
drivers/hid/hid-core.c:289:
report->size += parser->global.report_size * parser->global.report_count;
If `global.report_count` is zero, `report->size` gets increased by zero.
Is this working as intended? It seems weird to me.
Thank you,
Peilin Ye
next prev parent reply other threads:[~2020-07-20 19:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-18 23:12 [Linux-kernel-mentees] [PATCH v1] usbhid: Fix slab-out-of-bounds write in hiddev_ioctl_usage() Peilin Ye
2020-07-20 11:54 ` Dan Carpenter
2020-07-20 12:12 ` Dan Carpenter
2020-07-20 19:05 ` Peilin Ye [this message]
2020-07-20 19:16 ` Peilin Ye
2020-07-21 7:16 ` Dan Carpenter
2020-07-21 8:27 ` Greg Kroah-Hartman
2020-07-21 8:39 ` Dan Carpenter
2020-07-21 8:39 ` Peilin Ye
2020-07-20 19:52 ` [Linux-kernel-mentees] [PATCH v2] " Peilin Ye
2020-07-23 14:51 ` Dan Carpenter
2020-07-29 11:37 ` [Linux-kernel-mentees] [PATCH v2 RESEND] " Peilin Ye
2020-07-29 14:35 ` Dan Carpenter
2020-08-17 10:21 ` Jiri Kosina
2020-08-18 10:00 ` Peilin Ye
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