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>

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 309311b1faae18752a9bf24b0d350933aad4627c..cbaa8d776d83505c1d298b061970b1c44ef10456 100644 (file)
--- 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;