Add a checker for signature boundary in verifier

The 'signature_start' variable marks the location of the signature
from the end of a zip archive. And a boundary check is missing where
'signature_start' should be within the EOCD comment field. This causes
problems when sideloading a malicious package. Also add a corresponding

Bug: 31914369
Test: Verification fails correctly when sideloading on

Change-Id: I6ea96bf04dac5d8d4d6719e678d504f957b4d5c1
(cherry-picked from f69e6a9475983b2ad46729e44ab58d2b22cd74d0)
(cherry picked from commit 54ea136fded56810bf475885eb4bd7bf1b11f09c)
diff --git a/verifier.cpp b/verifier.cpp
index 61e5adf..bf7071d 100644
--- a/verifier.cpp
+++ b/verifier.cpp
@@ -144,6 +144,12 @@
     LOGI("comment is %zu bytes; signature %zu bytes from end\n",
          comment_size, signature_start);
+    if (signature_start > comment_size) {
+        LOGE("signature start: %zu is larger than comment size: %zu\n", signature_start,
+             comment_size);
+        return VERIFY_FAILURE;
+    }
     if (signature_start <= FOOTER_SIZE) {
         LOGE("Signature start is in the footer");
         return VERIFY_FAILURE;