linux-kernel - [PATCH 3.16 117/305] HID: hiddev: fix potential Spectre v1

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Message-ID: <lsq.1549201508.20288622@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jiri Kosina" <jkosina@...e.cz>, "Breno Leitao" <leitao@...ian.org>
Subject: [PATCH 3.16 117/305] HID: hiddev: fix potential Spectre v1

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Breno Leitao <leitao@...ian.org>

commit f11274396a538b31bc010f782e05c2ce3f804c13 upstream.

uref->usage_index can be indirectly controlled by userspace, hence leading
to a potential exploitation of the Spectre variant 1 vulnerability.

This field is used as an array index by the hiddev_ioctl_usage() function,
when 'cmd' is either HIDIOCGCOLLECTIONINDEX, HIDIOCGUSAGES or
HIDIOCSUSAGES.

For cmd == HIDIOCGCOLLECTIONINDEX case, uref->usage_index is compared to
field->maxusage and then used as an index to dereference field->usage
array. The same thing happens to the cmd == HIDIOC{G,S}USAGES cases, where
uref->usage_index is checked against an array maximum value and then it is
used as an index in an array.

This is a summary of the HIDIOCGCOLLECTIONINDEX case, which matches the
traditional Spectre V1 first load:

	copy_from_user(uref, user_arg, sizeof(*uref))
	if (uref->usage_index >= field->maxusage)
		goto inval;
	i = field->usage[uref->usage_index].collection_index;
	return i;

This patch fixes this by sanitizing field uref->usage_index before using it
to index field->usage (HIDIOCGCOLLECTIONINDEX) or field->value in
HIDIOC{G,S}USAGES arrays, thus, avoiding speculation in the first load.

Signed-off-by: Breno Leitao <leitao@...ian.org>
--

v2: Contemplate cmd == HIDIOC{G,S}USAGES case
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/hid/usbhid/hiddev.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -521,14 +521,24 @@ static noinline int hiddev_ioctl_usage(s
 			if (cmd == HIDIOCGCOLLECTIONINDEX) {
 				if (uref->usage_index >= field->maxusage)
 					goto inval;
+				uref->usage_index =
+					array_index_nospec(uref->usage_index,
+							   field->maxusage);
 			} else if (uref->usage_index >= field->report_count)
 				goto inval;
 		}

-		if ((cmd == HIDIOCGUSAGES || cmd == HIDIOCSUSAGES) &&
-		    (uref_multi->num_values > HID_MAX_MULTI_USAGES ||
-		     uref->usage_index + uref_multi->num_values > field->report_count))
-			goto inval;
+		if (cmd == HIDIOCGUSAGES || cmd == HIDIOCSUSAGES) {
+			if (uref_multi->num_values > HID_MAX_MULTI_USAGES ||
+			    uref->usage_index + uref_multi->num_values >
+			    field->report_count)
+				goto inval;
+
+			uref->usage_index =
+				array_index_nospec(uref->usage_index,
+						   field->report_count -
+						   uref_multi->num_values);
+		}

 		switch (cmd) {
 		case HIDIOCGUSAGE: