Limit the number of PBKDF2 iterations when fuzzing.

(Otherwise the fuzzer will discover that it can trigger extremely large
amounts of computation and start timing out.)

BUG=oss-fuzz:9767

Change-Id: Ibc1da5a90da169c7caf522f792530d1020f8cb54
Reviewed-on: https://boringssl-review.googlesource.com/30404
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/pkcs8/pkcs8_x509.c

diff --git a/crypto/pkcs8/pkcs8_x509.c b/crypto/pkcs8/pkcs8_x509.c
index 5d7178a..811ab16 100644
--- a/crypto/pkcs8/pkcs8_x509.c
+++ b/crypto/pkcs8/pkcs8_x509.c
@@ -669,11 +669,17 @@
       goto err;
     }
 
+#if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
+    static const uint64_t kIterationsLimit = 1024;
+#else
+    static const uint64_t kIterationsLimit = UINT_MAX;
+#endif
+
     // The iteration count is optional and the default is one.
     uint64_t iterations = 1;
     if (CBS_len(&mac_data) > 0) {
       if (!CBS_get_asn1_uint64(&mac_data, &iterations) ||
-          iterations > UINT_MAX) {
+          iterations > kIterationsLimit) {
         OPENSSL_PUT_ERROR(PKCS8, PKCS8_R_BAD_PKCS12_DATA);
         goto err;
       }