DO NOT MERGE A security fix to check buffer length in l2c_lcc_proc_pdu

Add check to make sure that data buffer is big enough to read the 2
bytes for length.

Also, fix a regression from the previous CL that checks the buffer length
before doing a memcpy. The previous check is too strict causing valid
sized buffers to be rejected. The length check is incorrect and off by the header size.

Bug: 120665616
Test: Run the SL4A Test for LE CoC, BleCoCTest
Merged-In: I30b7a8af11d3a5f974cb39e06b0e3463bebc8e9a
Change-Id: I30b7a8af11d3a5f974cb39e06b0e3463bebc8e9a
(cherry picked from commit fcb1994de1f6ee34b8dc6804a2b32e20bf138073)
(cherry picked from commit 1f1d8b97d80d25023c4c7b04d2aa18d367f4158d)
(cherry picked from commit c117a1c951c65033987ed51d53407b359204c187)
diff --git a/stack/l2cap/l2c_fcr.cc b/stack/l2cap/l2c_fcr.cc
index 8326e4d..88503fb 100644
--- a/stack/l2cap/l2c_fcr.cc
+++ b/stack/l2cap/l2c_fcr.cc
@@ -833,7 +833,16 @@
   }
 
   if (p_ccb->is_first_seg) {
+    if (p_buf->len < sizeof(sdu_length)) {
+      L2CAP_TRACE_ERROR("%s: buffer length=%d too small. Need at least 2.",
+                        __func__, p_buf->len);
+      android_errorWriteWithInfoLog(0x534e4554, "120665616", -1, NULL, 0);
+      /* Discard the buffer */
+      osi_free(p_buf);
+      return;
+    }
     STREAM_TO_UINT16(sdu_length, p);
+
     /* Check the SDU Length with local MTU size */
     if (sdu_length > p_ccb->local_conn_cfg.mtu) {
       /* Discard the buffer */
@@ -841,6 +850,9 @@
       return;
     }
 
+    p_buf->len -= sizeof(sdu_length);
+    p_buf->offset += sizeof(sdu_length);
+
     if (sdu_length < p_buf->len) {
       L2CAP_TRACE_ERROR("%s: Invalid sdu_length: %d", __func__, sdu_length);
       android_errorWriteWithInfoLog(0x534e4554, "112321180", -1, NULL, 0);
@@ -859,8 +871,6 @@
     p_data->len = 0;
     p_ccb->ble_sdu_length = sdu_length;
     L2CAP_TRACE_DEBUG("%s SDU Length = %d", __func__, sdu_length);
-    p_buf->len -= sizeof(sdu_length);
-    p_buf->offset += sizeof(sdu_length);
     p_data->offset = 0;
 
   } else {