[PATCH 2/2] staging: gdm724x: check for overflow in gdm_lte_netif_rx()

[Dan Carpenter <dan.carpenter@oracle.com>]

This code assumes that "len" is at least 62 bytes, but we need a check
to prevent a read overflow.

Fixes: 61e121047645 ("staging: gdm7240: adding LTE USB driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
There is a different place that does:

	ip_version = buf[0] >> 4;

Which assumes that "len" is one.  I think that should be checked in the
caller...  I didn't add a check here because I think it's the wrong
place but then I didn't add a check in the caller because I wasn't able
to test it.  I'm not really that worried about reading one element
beyond the end of the buffer.  If we get extremely unlucky it could
result in a crash...  Hopefully we will remember to look at this again
before moving this code out of staging.

#TODO:

 drivers/staging/gdm724x/gdm_lte.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/gdm724x/gdm_lte.c b/drivers/staging/gdm724x/gdm_lte.c
index a41af7aa74ec..bd5f87433404 100644
--- a/drivers/staging/gdm724x/gdm_lte.c
+++ b/drivers/staging/gdm724x/gdm_lte.c
@@ -611,10 +611,12 @@ static void gdm_lte_netif_rx(struct net_device *dev, char *buf,
 						  * bytes (99,130,83,99 dec)
 						  */
 			} __packed;
-			void *addr = buf + sizeof(struct iphdr) +
-				sizeof(struct udphdr) +
-				offsetof(struct dhcp_packet, chaddr);
-			ether_addr_copy(nic->dest_mac_addr, addr);
+			int offset = sizeof(struct iphdr) +
+				     sizeof(struct udphdr) +
+				     offsetof(struct dhcp_packet, chaddr);
+			if (offset + ETH_ALEN > len)
+				return;
+			ether_addr_copy(nic->dest_mac_addr, buf + offset);
 		}
 	}
 
-- 
2.30.2