mrs: make quarantine size tuneable

The environmental variables _RUNTIME_QUARANTINE_NUMERATOR and
_RUNTIME_QUARANTINE_DENOMINATOR can now override compiled defaults for
QUARANTINE_NUMERATOR and QUARANTINE_DENOMINATOR.

Author: brooksdavis

lib/libc/stdlib/malloc/mrs/mrs.c

@@ -139,6 +139,11 @@ extern void snmalloc_flush_message_queue(void);
 #define	MALLOC_NOBOUND_CHERI_POINTERS \
 	"_RUNTIME_NOBOUND_CHERI_POINTERS"
 
+#define	MALLOC_QUARANTINE_DENOMINATOR_ENV \
+	"_RUNTIME_QUARANTINE_DENOMINATOR"
+#define	MALLOC_QUARANTINE_NUMERATOR_ENV \
+	"_RUNTIME_QUARANTINE_NUMERATOR"
+
 /*
  * Different allocators give their strong symbols different names.  Hide
  * this implementation detail being the REAL() macro.
@@ -1316,6 +1321,33 @@ mrs_init_impl_locked(void)
 		exit(7);
 	}
 
+	if (!issetugid()) {
+		char *envstr, *end;
+		if ((envstr = getenv(MALLOC_QUARANTINE_DENOMINATOR_ENV)) !=
+		    NULL) {
+			errno = 0;
+			quarantine_denominator = strtoul(envstr, &end, 0);
+			if (*end != '\0' ||
+			    (quarantine_denominator == ULONG_MAX &&
+			     errno == ERANGE)) {
+				mrs_puts("invalid "
+				    MALLOC_QUARANTINE_DENOMINATOR_ENV "\n");
+				exit(7);
+			}
+		}
+		if ((envstr = getenv(MALLOC_QUARANTINE_NUMERATOR_ENV)) !=
+		    NULL) {
+			errno = 0;
+			quarantine_numerator = strtoul(envstr, &end, 0);
+			if (*end != '\0' ||
+			    (quarantine_numerator == ULONG_MAX &&
+			     errno == ERANGE)) {
+				mrs_puts("invalid "
+				    MALLOC_QUARANTINE_NUMERATOR_ENV "\n");
+				exit(7);
+			}
+		}
+	}
 	if (quarantine_denominator == 0) {
 		mrs_puts("quarantine_denominator can not be 0\n");
 		exit(7);