crypto: use correct derived key size when timing pbkdf

Currently when timing the pbkdf algorithm a fixed key
size of 32 bytes is used. This results in inaccurate
timings for certain hashes depending on their digest
size. For example when using sha1 with aes-256, this
causes us to measure time for the master key digest
doing 2 sha1 operations per iteration, instead of 1.

Instead we should pass in the desired key size to the
timing routine that matches the key size that will be
used for real later.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/crypto/pbkdf.c b/crypto/pbkdf.c
index e3915058fb..f22e71d183 100644
--- a/crypto/pbkdf.c
+++ b/crypto/pbkdf.c
@@ -65,13 +65,16 @@ static int qcrypto_pbkdf2_get_thread_cpu(unsigned long long *val_ms,
 uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
                                     const uint8_t *key, size_t nkey,
                                     const uint8_t *salt, size_t nsalt,
+                                    size_t nout,
                                     Error **errp)
 {
     uint64_t ret = -1;
-    uint8_t out[32];
+    uint8_t *out;
     uint64_t iterations = (1 << 15);
     unsigned long long delta_ms, start_ms, end_ms;
 
+    out = g_new(uint8_t, nout);
+
     while (1) {
         if (qcrypto_pbkdf2_get_thread_cpu(&start_ms, errp) < 0) {
             goto cleanup;
@@ -80,7 +83,7 @@ uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
                            key, nkey,
                            salt, nsalt,
                            iterations,
-                           out, sizeof(out),
+                           out, nout,
                            errp) < 0) {
             goto cleanup;
         }
@@ -104,6 +107,7 @@ uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
     ret = iterations;
 
  cleanup:
-    memset(out, 0, sizeof(out));
+    memset(out, 0, nout);
+    g_free(out);
     return ret;
 }