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ab91405a AM |
1 | From 517a7737dccb9837b4d9d751e64ae7b60948ef2e Mon Sep 17 00:00:00 2001 |
2 | From: Tomas Mraz <tomas@openssl.org> | |
3 | Date: Wed, 2 Feb 2022 17:47:26 +0100 | |
4 | Subject: [PATCH] Replace size check with more meaningful pubkey check | |
5 | ||
6 | It does not make sense to check the size because this | |
7 | function can be used in other contexts than in TLS-1.3 and | |
8 | the value might not be padded to the size of p. | |
9 | ||
10 | However it makes sense to do the partial pubkey check because | |
11 | there is no valid reason having the pubkey value outside the | |
12 | 1 < pubkey < p-1 bounds. | |
13 | ||
14 | Fixes #15465 | |
15 | --- | |
16 | crypto/dh/dh_key.c | 11 ++++------- | |
17 | 1 file changed, 4 insertions(+), 7 deletions(-) | |
18 | ||
19 | diff --git a/crypto/dh/dh_key.c b/crypto/dh/dh_key.c | |
20 | index 6b8cd550f25f..c78ed618bf83 100644 | |
21 | --- a/crypto/dh/dh_key.c | |
22 | +++ b/crypto/dh/dh_key.c | |
23 | @@ -375,20 +375,17 @@ int ossl_dh_buf2key(DH *dh, const unsigned char *buf, size_t len) | |
24 | int err_reason = DH_R_BN_ERROR; | |
25 | BIGNUM *pubkey = NULL; | |
26 | const BIGNUM *p; | |
27 | - size_t p_size; | |
28 | + int ret; | |
29 | ||
30 | if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL) | |
31 | goto err; | |
32 | DH_get0_pqg(dh, &p, NULL, NULL); | |
33 | - if (p == NULL || (p_size = BN_num_bytes(p)) == 0) { | |
34 | + if (p == NULL || BN_num_bytes(p) == 0) { | |
35 | err_reason = DH_R_NO_PARAMETERS_SET; | |
36 | goto err; | |
37 | } | |
38 | - /* | |
39 | - * As per Section 4.2.8.1 of RFC 8446 fail if DHE's | |
40 | - * public key is of size not equal to size of p | |
41 | - */ | |
42 | - if (BN_is_zero(pubkey) || p_size != len) { | |
43 | + /* Prevent small subgroup attacks per RFC 8446 Section 4.2.8.1 */ | |
44 | + if (!ossl_dh_check_pub_key_partial(dh, pubkey, &ret)) { | |
45 | err_reason = DH_R_INVALID_PUBKEY; | |
46 | goto err; | |
47 | } |