firewire: net: guard against rx buffer overflows

The IP-over-1394 driver firewire-net lacked input validation when
handling incoming fragmented datagrams.  A maliciously formed fragment
with a respectively large datagram_offset would cause a memcpy past the
datagram buffer.

So, drop any packets carrying a fragment with offset + length larger
than datagram_size.

In addition, ensure that
  - GASP header, unfragmented encapsulation header, or fragment
    encapsulation header actually exists before we access it,
  - the encapsulated datagram or fragment is of nonzero size.

Reported-by: Eyal Itkin <eyal.itkin@gmail.com>
Reviewed-by: Eyal Itkin <eyal.itkin@gmail.com>
Fixes: CVE 2016-8633
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 35 insertions, 16 deletions

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 309311b1faae..cbaa8d776d83 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -578,6 +578,9 @@ static int fwnet_incoming_packet(struct fwnet_device *dev, __be32 *buf, int len,
         int retval;
         u16 ether_type;
 
+        if (len <= RFC2374_UNFRAG_HDR_SIZE)
+                return 0;
+
         hdr.w0 = be32_to_cpu(buf[0]);
         lf = fwnet_get_hdr_lf(&hdr);
         if (lf == RFC2374_HDR_UNFRAG) {
@@ -602,7 +605,12 @@ static int fwnet_incoming_packet(struct fwnet_device *dev, __be32 *buf, int len,
                 return fwnet_finish_incoming_packet(net, skb, source_node_id,
                                                     is_broadcast, ether_type);
         }
+
         /* A datagram fragment has been received, now the fun begins. */
+
+        if (len <= RFC2374_FRAG_HDR_SIZE)
+                return 0;
+
         hdr.w1 = ntohl(buf[1]);
         buf += 2;
         len -= RFC2374_FRAG_HDR_SIZE;
@@ -616,6 +624,9 @@ static int fwnet_incoming_packet(struct fwnet_device *dev, __be32 *buf, int len,
         datagram_label = fwnet_get_hdr_dgl(&hdr);
         dg_size = fwnet_get_hdr_dg_size(&hdr); /* ??? + 1 */
 
+        if (fg_off + len > dg_size)
+                return 0;
+
         spin_lock_irqsave(&dev->lock, flags);
 
         peer = fwnet_peer_find_by_node_id(dev, source_node_id, generation);
@@ -722,6 +733,22 @@ static void fwnet_receive_packet(struct fw_card *card, struct fw_request *r,
         fw_send_response(card, r, rcode);
 }
 
+static int gasp_source_id(__be32 *p)
+{
+        return be32_to_cpu(p[0]) >> 16;
+}
+
+static u32 gasp_specifier_id(__be32 *p)
+{
+        return (be32_to_cpu(p[0]) & 0xffff) << 8 |
+               (be32_to_cpu(p[1]) & 0xff000000) >> 24;
+}
+
+static u32 gasp_version(__be32 *p)
+{
+        return be32_to_cpu(p[1]) & 0xffffff;
+}
+
 static void fwnet_receive_broadcast(struct fw_iso_context *context,
                 u32 cycle, size_t header_length, void *header, void *data)
 {
@@ -731,9 +758,6 @@ static void fwnet_receive_broadcast(struct fw_iso_context *context,
         __be32 *buf_ptr;
         int retval;
         u32 length;
-        u16 source_node_id;
-        u32 specifier_id;
-        u32 ver;
         unsigned long offset;
         unsigned long flags;
 
@@ -750,22 +774,17 @@ static void fwnet_receive_broadcast(struct fw_iso_context *context,
 
         spin_unlock_irqrestore(&dev->lock, flags);
 
-        specifier_id =    (be32_to_cpu(buf_ptr[0]) & 0xffff) << 8
-                        | (be32_to_cpu(buf_ptr[1]) & 0xff000000) >> 24;
-        ver = be32_to_cpu(buf_ptr[1]) & 0xffffff;
-        source_node_id = be32_to_cpu(buf_ptr[0]) >> 16;
-
-        if (specifier_id == IANA_SPECIFIER_ID &&
-            (ver == RFC2734_SW_VERSION
+        if (length > IEEE1394_GASP_HDR_SIZE &&
+            gasp_specifier_id(buf_ptr) == IANA_SPECIFIER_ID &&
+            (gasp_version(buf_ptr) == RFC2734_SW_VERSION
 #if IS_ENABLED(CONFIG_IPV6)
-             || ver == RFC3146_SW_VERSION
+             || gasp_version(buf_ptr) == RFC3146_SW_VERSION
 #endif
-            )) {
-                buf_ptr += 2;
-                length -= IEEE1394_GASP_HDR_SIZE;
-                fwnet_incoming_packet(dev, buf_ptr, length, source_node_id,
+            ))
+                fwnet_incoming_packet(dev, buf_ptr + 2,
+                                      length - IEEE1394_GASP_HDR_SIZE,
+                                      gasp_source_id(buf_ptr),
                                       context->card->generation, true);
-        }
 
         packet.payload_length = dev->rcv_buffer_size;
         packet.interrupt = 1;