Check hidden API exemptions

Refuse to deal with newlines and null characters in
HiddenApiSettings.update(). Also disallow nulls in process start
arguments.

Bug: 316153291
Test: Treehugger for now
Change-Id: I83cd60e46407a4a082f9f3c80e937dbd522dbac4
(cherry picked from commit 7ba059e2)

core/java/android/os/ZygoteProcess.java

@@ -431,6 +431,8 @@ public class ZygoteProcess {
                 throw new ZygoteStartFailedEx("Embedded newlines not allowed");
             } else if (arg.indexOf('\r') >= 0) {
                 throw new ZygoteStartFailedEx("Embedded carriage returns not allowed");
+            } else if (arg.indexOf('\u0000') >= 0) {
+                throw new ZygoteStartFailedEx("Embedded nulls not allowed");
             }
         }
 
@@ -972,6 +974,14 @@ public class ZygoteProcess {
             return true;
         }
 
+        for (/* NonNull */ String s : mApiDenylistExemptions) {
+            // indexOf() is intrinsified and faster than contains().
+            if (s.indexOf('\n') >= 0 || s.indexOf('\r') >= 0 || s.indexOf('\u0000') >= 0) {
+                Slog.e(LOG_TAG, "Failed to set API denylist exemptions: Bad character");
+                mApiDenylistExemptions = Collections.emptyList();
+                return false;
+            }
+        }
         try {
             state.mZygoteOutputWriter.write(Integer.toString(mApiDenylistExemptions.size() + 1));
             state.mZygoteOutputWriter.newLine();