Add fuzzing!

Reviewed-by: Emilia Käsper <emilia@openssl.org>

1 files changed, 101 insertions, 0 deletions

diff --git a/fuzz/bndiv.c b/fuzz/bndiv.c
new file mode 100644
index 0000000000..c897de99b5
--- /dev/null
+++ b/fuzz/bndiv.c
@@ -0,0 +1,101 @@
+/*
+ * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL licenses, (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * https://www.openssl.org/source/license.html
+ * or in the file LICENSE in the source distribution.
+ */
+
+/*
+ * Confirm that if (d, r) = a / b, then b * d + r == a, and that sign(d) ==
+ * sign(a), and 0 <= r <= b
+ */
+
+#include <stdio.h>
+#include <openssl/bn.h>
+#include "fuzzer.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
+    int success = 0;
+    static BN_CTX *ctx;
+    static BIGNUM *b1;
+    static BIGNUM *b2;
+    static BIGNUM *b3;
+    static BIGNUM *b4;
+    static BIGNUM *b5;
+
+    if (ctx == NULL) {
+        b1 = BN_new();
+        b2 = BN_new();
+        b3 = BN_new();
+        b4 = BN_new();
+        b5 = BN_new();
+        ctx = BN_CTX_new();
+    }
+    // We are going to split the buffer in two, sizes l1 and l2, giving b1 and
+    // b2.
+    size_t l1 = 0, l2 = 0;
+    // s1 and s2 will be the signs for b1 and b2.
+    int s1 = 0, s2 = 0;
+    if (len > 0) {
+        --len;
+        // Use first byte to divide the remaining buffer into 3Fths. I admit
+        // this disallows some number sizes. If it matters, better ideas are
+        // welcome (Ben).
+        l1 = ((buf[0] & 0x3f) * len) / 0x3f;
+        s1 = buf[0] & 0x40;
+        s2 = buf[0] & 0x80;
+        ++buf;
+        l2 = len - l1;
+    }
+    OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
+    BN_set_negative(b1, s1);
+    OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
+    BN_set_negative(b2, s2);
+
+    // divide by 0 is an error
+    if (BN_is_zero(b2)) {
+        success = 1;
+        goto done;
+    }
+
+    OPENSSL_assert(BN_div(b3, b4, b1, b2, ctx));
+    if (BN_is_zero(b1))
+        success = BN_is_zero(b3) && BN_is_zero(b4);
+    else if (BN_is_negative(b1))
+        success = (BN_is_negative(b3) != BN_is_negative(b2) || BN_is_zero(b3))
+            && (BN_is_negative(b4) || BN_is_zero(b4));
+    else
+        success = (BN_is_negative(b3) == BN_is_negative(b2)  || BN_is_zero(b3))
+            && (!BN_is_negative(b4) || BN_is_zero(b4));
+    OPENSSL_assert(BN_mul(b5, b3, b2, ctx));
+    OPENSSL_assert(BN_add(b5, b5, b4));
+
+    success = success && BN_cmp(b5, b1) == 0;
+    if (!success) {
+        BN_print_fp(stdout, b1);
+        putchar('\n');
+        BN_print_fp(stdout, b2);
+        putchar('\n');
+        BN_print_fp(stdout, b3);
+        putchar('\n');
+        BN_print_fp(stdout, b4);
+        putchar('\n');
+        BN_print_fp(stdout, b5);
+        putchar('\n');
+        printf("%d %d %d %d %d %d %d\n", BN_is_negative(b1),
+               BN_is_negative(b2),
+               BN_is_negative(b3), BN_is_negative(b4), BN_is_zero(b4),
+               BN_is_negative(b3) != BN_is_negative(b2)
+               && (BN_is_negative(b4) || BN_is_zero(b4)),
+               BN_cmp(b5, b1));
+        puts("----\n");
+    }
+
+ done:
+    OPENSSL_assert(success);
+
+    return 0;
+}