[PATCH v2] usb: gadget: rndis: Prevent InformationBufferOffset manipulation

[Szymon Heidrich]

Prevent access to arbitrary memory locations in gen_ndis_set_resp
via manipulation of buf->InformationBufferOffset. Original
implementation permits manipulation of InformationBufferOffset to
exploit OID_GEN_CURRENT_PACKET_FILTER to set arbitrary memory contents
within a 32byte offset as the devices packet filter. The packet filter
value may be next retrieved using gen_ndis_query_resp so it is possible
to extract specific memory regions two bytes a time.

The rndis_query_response was not modified as neither the buffer offset
nor length passed to gen_ndis_query_resp is used.

Signed-off-by: Szymon Heidrich <szymon.heidrich at gmail.com>
---
V1 -> V2: Updated commit message

 drivers/usb/gadget/rndis.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/rndis.c b/drivers/usb/gadget/rndis.c
index 13c327ea38..3948f2cc9a 100644
--- a/drivers/usb/gadget/rndis.c
+++ b/drivers/usb/gadget/rndis.c
@@ -855,14 +855,17 @@ static int rndis_set_response(int configNr, rndis_set_msg_type *buf)
 	rndis_set_cmplt_type	*resp;
 	rndis_resp_t		*r;
 
+	BufLength = get_unaligned_le32(&buf->InformationBufferLength);
+	BufOffset = get_unaligned_le32(&buf->InformationBufferOffset);
+	if ((BufOffset > RNDIS_MAX_TOTAL_SIZE - 8) ||
+	    (BufLength > RNDIS_MAX_TOTAL_SIZE - 8 - BufOffset))
+		return -EINVAL;
+
 	r = rndis_add_response(configNr, sizeof(rndis_set_cmplt_type));
 	if (!r)
 		return -ENOMEM;
 	resp = (rndis_set_cmplt_type *) r->buf;
 
-	BufLength = get_unaligned_le32(&buf->InformationBufferLength);
-	BufOffset = get_unaligned_le32(&buf->InformationBufferOffset);
-
 #ifdef	VERBOSE
 	debug("%s: Length: %d\n", __func__, BufLength);
 	debug("%s: Offset: %d\n", __func__, BufOffset);
-- 
2.38.1