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-rw-r--r--debian/patches/60-auth-rsa_psk-side-step-potential-side-channel.patch229
1 files changed, 229 insertions, 0 deletions
diff --git a/debian/patches/60-auth-rsa_psk-side-step-potential-side-channel.patch b/debian/patches/60-auth-rsa_psk-side-step-potential-side-channel.patch
new file mode 100644
index 0000000..e85c16a
--- /dev/null
+++ b/debian/patches/60-auth-rsa_psk-side-step-potential-side-channel.patch
@@ -0,0 +1,229 @@
+From 29d6298d0b04cfff970b993915db71ba3f580b6d Mon Sep 17 00:00:00 2001
+From: Daiki Ueno <ueno@gnu.org>
+Date: Mon, 23 Oct 2023 09:26:57 +0900
+Subject: [PATCH] auth/rsa_psk: side-step potential side-channel
+
+This removes branching that depends on secret data, porting changes
+for regular RSA key exchange from
+4804febddc2ed958e5ae774de2a8f85edeeff538 and
+80a6ce8ddb02477cd724cd5b2944791aaddb702a. This also removes the
+allow_wrong_pms as it was used sorely to control debug output
+depending on the branching.
+
+Signed-off-by: Daiki Ueno <ueno@gnu.org>
+---
+ lib/auth/rsa.c | 2 +-
+ lib/auth/rsa_psk.c | 90 ++++++++++++++++++----------------------------
+ lib/gnutls_int.h | 4 ---
+ lib/priority.c | 1 -
+ 4 files changed, 35 insertions(+), 62 deletions(-)
+
+--- a/lib/auth/rsa.c
++++ b/lib/auth/rsa.c
+@@ -205,11 +205,11 @@ proc_rsa_client_kx(gnutls_session_t sess
+ gnutls_privkey_decrypt_data2(session->internals.selected_key,
+ 0, &ciphertext, session->key.key.data,
+ session->key.key.size);
+ /* After this point, any conditional on failure that cause differences
+ * in execution may create a timing or cache access pattern side
+- * channel that can be used as an oracle, so treat very carefully */
++ * channel that can be used as an oracle, so tread carefully */
+
+ /* Error handling logic:
+ * In case decryption fails then don't inform the peer. Just use the
+ * random key previously generated. (in order to avoid attack against
+ * pkcs-1 formatting).
+--- a/lib/auth/rsa_psk.c
++++ b/lib/auth/rsa_psk.c
+@@ -262,18 +262,17 @@ static int
+ _gnutls_proc_rsa_psk_client_kx(gnutls_session_t session, uint8_t * data,
+ size_t _data_size)
+ {
+ gnutls_datum_t username;
+ psk_auth_info_t info;
+- gnutls_datum_t plaintext;
+ gnutls_datum_t ciphertext;
+ gnutls_datum_t pwd_psk = { NULL, 0 };
+ int ret, dsize;
+- int randomize_key = 0;
+ ssize_t data_size = _data_size;
+ gnutls_psk_server_credentials_t cred;
+ gnutls_datum_t premaster_secret = { NULL, 0 };
++ volatile uint8_t ver_maj, ver_min;
+
+ cred = (gnutls_psk_server_credentials_t)
+ _gnutls_get_cred(session, GNUTLS_CRD_PSK);
+
+ if (cred == NULL) {
+@@ -327,75 +326,53 @@ _gnutls_proc_rsa_psk_client_kx(gnutls_se
+ gnutls_assert();
+ return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
+ }
+ ciphertext.size = dsize;
+
+- ret =
+- gnutls_privkey_decrypt_data(session->internals.selected_key, 0,
+- &ciphertext, &plaintext);
+- if (ret < 0 || plaintext.size != GNUTLS_MASTER_SIZE) {
+- /* In case decryption fails then don't inform
+- * the peer. Just use a random key. (in order to avoid
+- * attack against pkcs-1 formatting).
+- */
+- gnutls_assert();
+- _gnutls_debug_log
+- ("auth_rsa_psk: Possible PKCS #1 format attack\n");
+- if (ret >= 0) {
+- gnutls_free(plaintext.data);
+- }
+- randomize_key = 1;
+- } else {
+- /* If the secret was properly formatted, then
+- * check the version number.
+- */
+- if (_gnutls_get_adv_version_major(session) !=
+- plaintext.data[0]
+- || (session->internals.allow_wrong_pms == 0
+- && _gnutls_get_adv_version_minor(session) !=
+- plaintext.data[1])) {
+- /* No error is returned here, if the version number check
+- * fails. We proceed normally.
+- * That is to defend against the attack described in the paper
+- * "Attacking RSA-based sessions in SSL/TLS" by Vlastimil Klima,
+- * Ondej Pokorny and Tomas Rosa.
+- */
+- gnutls_assert();
+- _gnutls_debug_log
+- ("auth_rsa: Possible PKCS #1 version check format attack\n");
+- }
+- }
++ ver_maj = _gnutls_get_adv_version_major(session);
++ ver_min = _gnutls_get_adv_version_minor(session);
+
++ premaster_secret.data = gnutls_malloc(GNUTLS_MASTER_SIZE);
++ if (premaster_secret.data == NULL) {
+
+- if (randomize_key != 0) {
+- premaster_secret.size = GNUTLS_MASTER_SIZE;
+- premaster_secret.data =
+- gnutls_malloc(premaster_secret.size);
+- if (premaster_secret.data == NULL) {
+- gnutls_assert();
+- return GNUTLS_E_MEMORY_ERROR;
+- }
+-
+- /* we do not need strong random numbers here.
+- */
+- ret = gnutls_rnd(GNUTLS_RND_NONCE, premaster_secret.data,
+- premaster_secret.size);
+- if (ret < 0) {
+- gnutls_assert();
+- goto cleanup;
+- }
+- } else {
+- premaster_secret.data = plaintext.data;
+- premaster_secret.size = plaintext.size;
++ gnutls_assert();
++ return GNUTLS_E_MEMORY_ERROR;
+ }
++ premaster_secret.size = GNUTLS_MASTER_SIZE;
++
++ /* Fallback value when decryption fails. Needs to be unpredictable. */
++ ret = gnutls_rnd(GNUTLS_RND_NONCE, premaster_secret.data,
++ premaster_secret.size);
++ if (ret < 0) {
++ gnutls_assert();
++ goto cleanup;
++ }
++
++ gnutls_privkey_decrypt_data2(session->internals.selected_key, 0,
++ &ciphertext, premaster_secret.data,
++ premaster_secret.size);
++ /* After this point, any conditional on failure that cause differences
++ * in execution may create a timing or cache access pattern side
++ * channel that can be used as an oracle, so tread carefully */
++
++ /* Error handling logic:
++ * In case decryption fails then don't inform the peer. Just use the
++ * random key previously generated. (in order to avoid attack against
++ * pkcs-1 formatting).
++ *
++ * If we get version mismatches no error is returned either. We
++ * proceed normally. This is to defend against the attack described
++ * in the paper "Attacking RSA-based sessions in SSL/TLS" by
++ * Vlastimil Klima, Ondej Pokorny and Tomas Rosa.
++ */
+
+ /* This is here to avoid the version check attack
+ * discussed above.
+ */
+
+- premaster_secret.data[0] = _gnutls_get_adv_version_major(session);
+- premaster_secret.data[1] = _gnutls_get_adv_version_minor(session);
++ premaster_secret.data[0] = ver_maj;
++ premaster_secret.data[1] = ver_min;
+
+ /* find the key of this username
+ */
+ ret =
+ _gnutls_psk_pwd_find_entry(session, info->username, strlen(info->username), &pwd_psk);
+--- a/lib/gnutls_int.h
++++ b/lib/gnutls_int.h
+@@ -983,11 +983,10 @@ struct gnutls_priority_st {
+ bool _allow_large_records;
+ bool _allow_small_records;
+ bool _no_etm;
+ bool _no_ext_master_secret;
+ bool _allow_key_usage_violation;
+- bool _allow_wrong_pms;
+ bool _dumbfw;
+ unsigned int _dh_prime_bits; /* old (deprecated) variable */
+
+ DEF_ATOMIC_INT(usage_cnt);
+ };
+@@ -1001,20 +1000,18 @@ struct gnutls_priority_st {
+ (x)->allow_large_records = 1; \
+ (x)->allow_small_records = 1; \
+ (x)->no_etm = 1; \
+ (x)->no_ext_master_secret = 1; \
+ (x)->allow_key_usage_violation = 1; \
+- (x)->allow_wrong_pms = 1; \
+ (x)->dumbfw = 1
+
+ #define ENABLE_PRIO_COMPAT(x) \
+ (x)->_allow_large_records = 1; \
+ (x)->_allow_small_records = 1; \
+ (x)->_no_etm = 1; \
+ (x)->_no_ext_master_secret = 1; \
+ (x)->_allow_key_usage_violation = 1; \
+- (x)->_allow_wrong_pms = 1; \
+ (x)->_dumbfw = 1
+
+ /* DH and RSA parameters types.
+ */
+ typedef struct gnutls_dh_params_int {
+@@ -1135,11 +1132,10 @@ typedef struct {
+ bool allow_large_records;
+ bool allow_small_records;
+ bool no_etm;
+ bool no_ext_master_secret;
+ bool allow_key_usage_violation;
+- bool allow_wrong_pms;
+ bool dumbfw;
+
+ /* old (deprecated) variable. This is used for both srp_prime_bits
+ * and dh_prime_bits as they don't overlap */
+ /* For SRP: minimum bits to allow for SRP
+--- a/lib/priority.c
++++ b/lib/priority.c
+@@ -699,11 +699,10 @@ gnutls_priority_set(gnutls_session_t ses
+ COPY_TO_INTERNALS(allow_large_records);
+ COPY_TO_INTERNALS(allow_small_records);
+ COPY_TO_INTERNALS(no_etm);
+ COPY_TO_INTERNALS(no_ext_master_secret);
+ COPY_TO_INTERNALS(allow_key_usage_violation);
+- COPY_TO_INTERNALS(allow_wrong_pms);
+ COPY_TO_INTERNALS(dumbfw);
+ COPY_TO_INTERNALS(dh_prime_bits);
+
+ return 0;
+ }
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