Fix incorrect usage of vli_cmp when calculating the value of res.x. For signature verification to succeed, res.x must be the same as the r component of the signature which is in the range of [1..n-1] with 'n' being the order of the curve. Therefore, when res.x equals n calculate res.x = res.x - n as well. Signature verification could have previously unnecessarily failed in extremely rare cases.
Fixes: 4e6602916bc6 ("crypto: ecdsa - Add support for ECDSA signature verification") Cc: stable@vger.kernel.org Signed-off-by: Stefan Berger stefanb@linux.ibm.com --- crypto/ecdsa.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index b3a8a6b572ba..674ab9275366 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -120,8 +120,8 @@ static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, con /* res = u1*G + u2 * pub_key */ ecc_point_mult_shamir(&res, u1, &curve->g, u2, &ctx->pub_key, curve);
- /* res.x = res.x mod n (if res.x > order) */ - if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1)) + /* res.x = res.x mod n (if res.x >= order) */ + if (unlikely(vli_cmp(res.x, curve->n, ndigits) >= 0)) /* faster alternative for NIST p384, p256 & p192 */ vli_sub(res.x, res.x, curve->n, ndigits);