DO NOT MERGE: 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
test.

Bug: 31914369
Test: Verification fails correctly when sideloading recovery_test.zip on
angler.

Change-Id: I6ea96bf04dac5d8d4d6719e678d504f957b4d5c1
(cherry-picked from f69e6a9475)
(cherry picked from commit 54ea136fde)

verifier.cpp

@@ -79,6 +79,13 @@ int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys
     LOGI("comment is %d bytes; signature %d 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);
+        fclose(f);
+        return VERIFY_FAILURE;
+    }
+
     if (signature_start - FOOTER_SIZE < RSANUMBYTES) {
         // "signature" block isn't big enough to contain an RSA block.
         LOGE("signature is too short\n");