diff options
author | Nicola Tuveri <nic.tuv@gmail.com> | 2020-01-21 17:08:16 +0200 |
---|---|---|
committer | Nicola Tuveri <nic.tuv@gmail.com> | 2020-04-24 17:44:10 +0300 |
commit | 3655e35b78df095b367b3334b6515f6d9436fd95 (patch) | |
tree | a458f36969908679c19061951055c3074c0c8c34 | |
parent | 6a01f6f4b41d045e2a3abcb10163633d769db76a (diff) |
[BN] harden `BN_copy()` against leaks from memory accesses
`BN_copy()` (and indirectly `BN_dup()`) do not propagate the
`BN_FLG_CONSTTIME` flag: the propagation has been turned on and off a
few times in the past years, because in some conditions it has shown
unintended consequences in some code paths.
Without turning the propagation on once more, we can still improve
`BN_copy()` by avoiding to leak `src->top` in case `src` is flagged with
`BN_FLG_CONSTTIME`.
In this case we can instead use `src->dmax` as the number of words
allocated for `dst` and for the `memcpy` operation.
Barring compiler or runtime optimizations, if the caller provides `src`
flagged as const time and preallocated to a public size, no leak should
happen due to the copy operation.
(cherry picked from commit 2d9167ed0b588dacbdd0303fb6041ffe1d8b3a92)
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11127)
-rw-r--r-- | crypto/bn/bn_lib.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c index 86d4956c8a..759d4c70ed 100644 --- a/crypto/bn/bn_lib.c +++ b/crypto/bn/bn_lib.c @@ -322,15 +322,19 @@ BIGNUM *BN_dup(const BIGNUM *a) BIGNUM *BN_copy(BIGNUM *a, const BIGNUM *b) { + int bn_words; + bn_check_top(b); + bn_words = BN_get_flags(b, BN_FLG_CONSTTIME) ? b->dmax : b->top; + if (a == b) return a; - if (bn_wexpand(a, b->top) == NULL) + if (bn_wexpand(a, bn_words) == NULL) return NULL; if (b->top > 0) - memcpy(a->d, b->d, sizeof(b->d[0]) * b->top); + memcpy(a->d, b->d, sizeof(b->d[0]) * bn_words); a->neg = b->neg; a->top = b->top; |