Improve Malloc Failure Test

Allow 2 digits after the comma in percentage in OPENSSL_MALLOC_FAILURES.
Add OPENSSL_MALLOC_SEED to allow for some randomization.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22127)

crypto/mem.c

@@ -100,6 +100,9 @@ void CRYPTO_get_alloc_counts(int *mcount, int *rcount, int *fcount)
  *    or    100;100@25;0
  * This means 100 mallocs succeed, then next 100 fail 25% of the time, and
  * all remaining (count is zero) succeed.
+ * The failure percentge can have 2 digits after the comma.  For example:
+ *          0@0.01
+ * This means 0.01% of all allocations will fail.
  */
 static void parseit(void)
 {
@@ -112,7 +115,7 @@ static void parseit(void)
     /* Get the count (atol will stop at the @ if there), and percentage */
     md_count = atol(md_failstring);
     atsign = strchr(md_failstring, '@');
-    md_fail_percent = atsign == NULL ? 0 : atoi(atsign + 1);
+    md_fail_percent = atsign == NULL ? 0 : (int)(atof(atsign + 1) * 100 + 0.5);
 
     if (semi != NULL)
         md_failstring = semi;
@@ -131,7 +134,7 @@ static void parseit(void)
  */
 static int shouldfail(void)
 {
-    int roll = (int)(random() % 100);
+    int roll = (int)(random() % 10000);
     int shoulditfail = roll < md_fail_percent;
 # ifndef _WIN32
 /* suppressed on Windows as POSIX-like file descriptors are non-inheritable */
@@ -165,6 +168,8 @@ void ossl_malloc_setup_failures(void)
         parseit();
     if ((cp = getenv("OPENSSL_MALLOC_FD")) != NULL)
         md_tracefd = atoi(cp);
+    if ((cp = getenv("OPENSSL_MALLOC_SEED")) != NULL)
+        srandom(atoi(cp));
 }
 #endif