logcat: add sanity check

Sanity check that the length we get back from the kernel matches
how much data we actually received.

Change-Id: I5cfd80321ab41459bb514dfde2da57413a7bd9e6
diff --git a/logcat/logcat.cpp b/logcat/logcat.cpp
index 4cd2151..ae56c41 100644
--- a/logcat/logcat.cpp
+++ b/logcat/logcat.cpp
@@ -296,6 +296,11 @@
                         fprintf(stderr, "read: Unexpected EOF!\n");
                         exit(EXIT_FAILURE);
                     }
+                    else if (entry->entry.len != ret - sizeof(struct logger_entry)) {
+                        fprintf(stderr, "read: unexpected length. Expected %d, got %d\n",
+                                entry->entry.len, ret - sizeof(struct logger_entry));
+                        exit(EXIT_FAILURE);
+                    }
 
                     entry->entry.msg[entry->entry.len] = '\0';