Test for constant-time flag leakage in BN_CTX
This commit adds a simple unit test to make sure that the constant-time flag does not "leak" among BN_CTX frames: - test_ctx_consttime_flag() initializes (and later frees before returning) a BN_CTX object, then it calls in sequence test_ctx_set_ct_flag() and test_ctx_check_ct_flag() using the same BN_CTX object. The process is run twice, once with a "normal" BN_CTX_new() object, then with a BN_CTX_secure_new() one. - test_ctx_set_ct_flag() starts a frame in the given BN_CTX and sets the BN_FLG_CONSTTIME flag on some of the BIGNUMs obtained from the frame before ending it. - test_ctx_check_ct_flag() then starts a new frame and gets a number of BIGNUMs from it. In absence of leaks, none of the BIGNUMs in the new frame should have BN_FLG_CONSTTIME set. In actual BN_CTX usage inside libcrypto the leak could happen at any depth level in the BN_CTX stack, with varying results depending on the patterns of sibling trees of nested function calls sharing the same BN_CTX object, and the effect of unintended BN_FLG_CONSTTIME on the called BN_* functions. This simple unit test abstracts away this complexity and verifies that the leak does not happen between two sibling functions sharing the same BN_CTX object at the same level of nesting. Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/8253)
This commit is contained in:
Nicola Tuveri
parent
0b76ce99aa
commit
fe16ae5f95
1 changed files with 122 additions and 39 deletions
161
test/bntest.c
161
test/bntest.c
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@ -1,5 +1,5 @@
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/*
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* Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
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* Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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@ -123,7 +123,7 @@ static int getint(STANZA *s, int *out, const char *attribute)
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*out = (int)word;
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st = 1;
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err:
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err:
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BN_free(ret);
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return st;
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}
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@ -138,7 +138,6 @@ static int equalBN(const char *op, const BIGNUM *expected, const BIGNUM *actual)
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return 0;
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}
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/*
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* Return a "random" flag for if a BN should be negated.
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*/
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@ -150,7 +149,6 @@ static int rand_neg(void)
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return sign[(neg++) % 8];
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}
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static int test_swap(void)
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{
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BIGNUM *a = NULL, *b = NULL, *c = NULL, *d = NULL;
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@ -166,7 +164,7 @@ static int test_swap(void)
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BN_bntest_rand(b, 1024, 1, 0);
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BN_copy(c, a);
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BN_copy(d, b);
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top = BN_num_bits(a)/BN_BITS2;
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top = BN_num_bits(a) / BN_BITS2;
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/* regular swap */
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BN_swap(a, b);
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@ -252,14 +250,13 @@ static int test_sub(void)
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goto err;
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(c);
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return st;
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}
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static int test_div_recip(void)
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{
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BIGNUM *a = NULL, *b = NULL, *c = NULL, *d = NULL, *e = NULL;
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@ -293,7 +290,7 @@ static int test_div_recip(void)
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goto err;
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(c);
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@ -303,7 +300,6 @@ err:
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return st;
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}
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static int test_mod(void)
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{
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BIGNUM *a = NULL, *b = NULL, *c = NULL, *d = NULL, *e = NULL;
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@ -328,7 +324,7 @@ static int test_mod(void)
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goto err;
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(c);
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@ -573,7 +569,7 @@ static int test_modexp_mont5(void)
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st = 1;
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err:
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err:
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BN_MONT_CTX_free(mont);
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BN_free(a);
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BN_free(p);
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@ -1141,7 +1137,7 @@ static int file_sum(STANZA *s)
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(sum);
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@ -1190,7 +1186,7 @@ static int file_lshift1(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(lshift1);
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BN_free(zero);
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@ -1219,7 +1215,7 @@ static int file_lshift(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(lshift);
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BN_free(ret);
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@ -1249,7 +1245,7 @@ static int file_rshift(STANZA *s)
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(rshift);
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BN_free(ret);
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@ -1306,7 +1302,7 @@ static int file_square(STANZA *s)
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#endif
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(square);
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BN_free(zero);
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@ -1343,7 +1339,7 @@ static int file_product(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(product);
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@ -1426,7 +1422,7 @@ static int file_quotient(STANZA *s)
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(quotient);
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@ -1480,7 +1476,7 @@ static int file_modmul(STANZA *s)
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}
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(m);
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@ -1532,7 +1528,7 @@ static int file_modexp(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(c);
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@ -1560,7 +1556,7 @@ static int file_exp(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(e);
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BN_free(exp);
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@ -1591,7 +1587,7 @@ static int file_modsqrt(STANZA *s)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(p);
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BN_free(mod_sqrt);
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@ -1621,8 +1617,8 @@ static int test_bn2padded(void)
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/* Test a random numbers at various byte lengths. */
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for (size_t bytes = 128 - 7; bytes <= 128; bytes++) {
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#define TOP_BIT_ON 0
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#define BOTTOM_BIT_NOTOUCH 0
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# define TOP_BIT_ON 0
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# define BOTTOM_BIT_NOTOUCH 0
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if (!TEST_true(BN_rand(n, bytes * 8, TOP_BIT_ON, BOTTOM_BIT_NOTOUCH)))
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goto err;
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if (!TEST_int_eq(BN_num_bytes(n),A) bytes
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@ -1653,7 +1649,7 @@ static int test_bn2padded(void)
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}
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st = 1;
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err:
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err:
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BN_free(n);
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return st;
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#else
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@ -1725,7 +1721,7 @@ static int test_dec2bn(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(bn);
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return st;
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}
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@ -1791,7 +1787,7 @@ static int test_hex2bn(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(bn);
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return st;
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}
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@ -1845,7 +1841,7 @@ static int test_asc2bn(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(bn);
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return st;
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}
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@ -1889,7 +1885,7 @@ static int test_mpi(int i)
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BN_free(bn2);
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st = 1;
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err:
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err:
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BN_free(bn);
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return st;
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}
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@ -1915,7 +1911,7 @@ static int test_rand(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(bn);
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return st;
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}
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@ -1979,7 +1975,7 @@ static int test_negzero(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(c);
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@ -2020,7 +2016,7 @@ static int test_badmod(void)
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ERR_clear_error();
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if (!TEST_false(BN_mod_exp_mont_consttime(a, BN_value_one(), BN_value_one(),
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zero, ctx, NULL)))
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zero, ctx, NULL)))
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goto err;
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ERR_clear_error();
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@ -2042,12 +2038,12 @@ static int test_badmod(void)
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ERR_clear_error();
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if (!TEST_false(BN_mod_exp_mont_consttime(a, BN_value_one(), BN_value_one(),
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b, ctx, NULL)))
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b, ctx, NULL)))
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goto err;
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ERR_clear_error();
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st = 1;
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err:
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err:
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BN_free(a);
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BN_free(b);
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BN_free(zero);
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@ -2081,7 +2077,7 @@ static int test_expmodzero(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(zero);
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BN_free(a);
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BN_free(r);
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@ -2127,7 +2123,7 @@ static int test_expmodone(void)
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}
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ret = 1;
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err:
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err:
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BN_free(r);
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BN_free(a);
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BN_free(p);
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@ -2148,7 +2144,7 @@ static int test_smallprime(void)
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goto err;
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st = 1;
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err:
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err:
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BN_free(r);
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return st;
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}
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@ -2172,7 +2168,7 @@ static int test_is_prime(int i)
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}
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ret = 1;
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err:
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err:
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BN_free(r);
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return ret;
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}
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@ -2195,11 +2191,97 @@ static int test_not_prime(int i)
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}
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ret = 1;
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err:
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err:
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BN_free(r);
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return ret;
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}
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static int test_ctx_set_ct_flag(BN_CTX *c)
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{
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int st = 0;
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size_t i;
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BIGNUM *b[15];
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BN_CTX_start(c);
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for (i = 0; i < OSSL_NELEM(b); i++) {
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if (!TEST_ptr(b[i] = BN_CTX_get(c)))
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goto err;
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if (i % 2 == 1)
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BN_set_flags(b[i], BN_FLG_CONSTTIME);
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}
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st = 1;
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err:
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BN_CTX_end(c);
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return st;
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}
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static int test_ctx_check_ct_flag(BN_CTX *c)
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{
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int st = 0;
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size_t i;
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BIGNUM *b[30];
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BN_CTX_start(c);
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for (i = 0; i < OSSL_NELEM(b); i++) {
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if (!TEST_ptr(b[i] = BN_CTX_get(c)))
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goto err;
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if (!TEST_false(BN_get_flags(b[i], BN_FLG_CONSTTIME)))
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goto err;
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}
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st = 1;
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err:
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BN_CTX_end(c);
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return st;
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}
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static int test_ctx_consttime_flag(void)
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{
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/*-
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* The constant-time flag should not "leak" among BN_CTX frames:
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*
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* - test_ctx_set_ct_flag() starts a frame in the given BN_CTX and
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* sets the BN_FLG_CONSTTIME flag on some of the BIGNUMs obtained
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* from the frame before ending it.
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* - test_ctx_check_ct_flag() then starts a new frame and gets a
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* number of BIGNUMs from it. In absence of leaks, none of the
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* BIGNUMs in the new frame should have BN_FLG_CONSTTIME set.
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*
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* In actual BN_CTX usage inside libcrypto the leak could happen at
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* any depth level in the BN_CTX stack, with varying results
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* depending on the patterns of sibling trees of nested function
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* calls sharing the same BN_CTX object, and the effect of
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* unintended BN_FLG_CONSTTIME on the called BN_* functions.
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*
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* This simple unit test abstracts away this complexity and verifies
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* that the leak does not happen between two sibling functions
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* sharing the same BN_CTX object at the same level of nesting.
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*
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*/
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BN_CTX *nctx = NULL;
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BN_CTX *sctx = NULL;
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size_t i = 0;
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int st = 0;
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if (!TEST_ptr(nctx = BN_CTX_new())
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|| !TEST_ptr(sctx = BN_CTX_secure_new()))
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goto err;
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for (i = 0; i < 2; i++) {
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BN_CTX *c = i == 0 ? nctx : sctx;
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if (!TEST_true(test_ctx_set_ct_flag(c))
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|| !TEST_true(test_ctx_check_ct_flag(c)))
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goto err;
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}
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st = 1;
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err:
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BN_CTX_free(nctx);
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BN_CTX_free(sctx);
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return st;
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}
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static int file_test_run(STANZA *s)
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{
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static const FILETEST filetests[] = {
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@ -2298,6 +2380,7 @@ int setup_tests(void)
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ADD_TEST(test_expmodone);
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ADD_TEST(test_smallprime);
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ADD_TEST(test_swap);
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ADD_TEST(test_ctx_consttime_flag);
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#ifndef OPENSSL_NO_EC2M
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ADD_TEST(test_gf2m_add);
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ADD_TEST(test_gf2m_mod);
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Reference in a new issue