diff options
Diffstat (limited to 'crypto/bn')
| -rw-r--r-- | crypto/bn/bn_ctx.c | 4 | ||||
| -rw-r--r-- | crypto/bn/bn_lib.c | 3 | ||||
| -rw-r--r-- | crypto/bn/bntest.c | 101 |
3 files changed, 107 insertions, 1 deletions
diff --git a/crypto/bn/bn_ctx.c b/crypto/bn/bn_ctx.c index 526c6a0..d18eedb 100644 --- a/crypto/bn/bn_ctx.c +++ b/crypto/bn/bn_ctx.c @@ -1,7 +1,7 @@ /* crypto/bn/bn_ctx.c */ /* Written by Ulf Moeller for the OpenSSL project. */ /* ==================================================================== - * Copyright (c) 1998-2004 The OpenSSL Project. All rights reserved. + * Copyright (c) 1998-2019 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions @@ -299,6 +299,8 @@ BIGNUM *BN_CTX_get(BN_CTX *ctx) } /* OK, make sure the returned bignum is "zero" */ BN_zero(ret); + /* clear BN_FLG_CONSTTIME if leaked from previous frames */ + ret->flags &= (~BN_FLG_CONSTTIME); ctx->used++; CTXDBG_RET(ctx, ret); return ret; diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c index 9b95e5f..2a84698 100644 --- a/crypto/bn/bn_lib.c +++ b/crypto/bn/bn_lib.c @@ -836,6 +836,9 @@ int bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n) int i; BN_ULONG aa, bb; + if (n == 0) + return 0; + aa = a[n - 1]; bb = b[n - 1]; if (aa != bb) diff --git a/crypto/bn/bntest.c b/crypto/bn/bntest.c index abe5dbe..75aa707 100644 --- a/crypto/bn/bntest.c +++ b/crypto/bn/bntest.c @@ -89,6 +89,10 @@ #include <openssl/x509.h> #include <openssl/err.h> +#ifndef OSSL_NELEM +# define OSSL_NELEM(x) (sizeof(x)/sizeof(x[0])) +#endif + const int num0 = 100; /* number of tests */ const int num1 = 50; /* additional tests for some functions */ const int num2 = 5; /* number of tests for slow functions */ @@ -123,6 +127,7 @@ int test_gf2m_mod_solve_quad(BIO *bp, BN_CTX *ctx); int test_kron(BIO *bp, BN_CTX *ctx); int test_sqrt(BIO *bp, BN_CTX *ctx); int rand_neg(void); +static int test_ctx_consttime_flag(void); static int results = 0; static unsigned char lst[] = @@ -330,6 +335,15 @@ int main(int argc, char *argv[]) goto err; (void)BIO_flush(out); #endif + + /* silently flush any pre-existing error on the stack */ + ERR_clear_error(); + + message(out, "BN_CTX_get BN_FLG_CONSTTIME"); + if (!test_ctx_consttime_flag()) + goto err; + (void)BIO_flush(out); + BN_CTX_free(ctx); BIO_free(out); @@ -2158,3 +2172,90 @@ int rand_neg(void) return (sign[(neg++) % 8]); } + +static int test_ctx_set_ct_flag(BN_CTX *c) +{ + int st = 0; + size_t i; + BIGNUM *b[15]; + + BN_CTX_start(c); + for (i = 0; i < OSSL_NELEM(b); i++) { + if (NULL == (b[i] = BN_CTX_get(c))) { + fprintf(stderr, "ERROR: BN_CTX_get() failed.\n"); + goto err; + } + if (i % 2 == 1) + BN_set_flags(b[i], BN_FLG_CONSTTIME); + } + + st = 1; + err: + BN_CTX_end(c); + return st; +} + +static int test_ctx_check_ct_flag(BN_CTX *c) +{ + int st = 0; + size_t i; + BIGNUM *b[30]; + + BN_CTX_start(c); + for (i = 0; i < OSSL_NELEM(b); i++) { + if (NULL == (b[i] = BN_CTX_get(c))) { + fprintf(stderr, "ERROR: BN_CTX_get() failed.\n"); + goto err; + } + if (BN_get_flags(b[i], BN_FLG_CONSTTIME) != 0) { + fprintf(stderr, "ERROR: BN_FLG_CONSTTIME should not be set.\n"); + goto err; + } + } + + st = 1; + err: + BN_CTX_end(c); + return st; +} + +static int test_ctx_consttime_flag(void) +{ + /*- + * The constant-time flag should not "leak" among BN_CTX frames: + * + * - 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. + * + */ + BN_CTX *c = NULL; + int st = 0; + + if (NULL == (c = BN_CTX_new())) { + fprintf(stderr, "ERROR: BN_CTX_new() failed.\n"); + goto err; + } + + if (!test_ctx_set_ct_flag(c) + || !test_ctx_check_ct_flag(c)) + goto err; + + st = 1; + err: + BN_CTX_free(c); + return st; +} |