Backport of:
From ed5095ed94281989e103c72e032200b83be37878 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Thu, 6 Oct 2022 00:49:10 +0200
Subject: [PATCH] strcase: add and use Curl_timestrcmp
This is a strcmp() alternative function for comparing "secrets",
designed to take the same time no matter the content to not leak
match/non-match info to observers based on how fast it is.
The time this function takes is only a function of the shortest input
string.
Reported-by: Trail of Bits
Closes #9658
---
lib/netrc.c | 6 +++---
lib/strcase.c | 22 ++++++++++++++++++++++
lib/strcase.h | 1 +
lib/url.c | 34 +++++++++++++---------------------
lib/vauth/digest_sspi.c | 4 ++--
lib/vtls/vtls.c | 4 ++--
6 files changed, 43 insertions(+), 28 deletions(-)
--- a/lib/netrc.c
+++ b/lib/netrc.c
@@ -123,9 +123,9 @@ static int parsenetrc(const char *host,
/* we are now parsing sub-keywords concerning "our" host */
if(state_login) {
if(specific_login) {
- state_our_login = strcasecompare(login, tok);
+ state_our_login = !Curl_timestrcmp(login, tok);
}
- else if(!login || strcmp(login, tok)) {
+ else if(!login || Curl_timestrcmp(login, tok)) {
if(login_alloc) {
free(login);
login_alloc = FALSE;
@@ -141,7 +141,7 @@ static int parsenetrc(const char *host,
}
else if(state_password) {
if((state_our_login || !specific_login)
- && (!password || strcmp(password, tok))) {
+ && (!password || Curl_timestrcmp(password, tok))) {
if(password_alloc) {
free(password);
password_alloc = FALSE;
--- a/lib/strcase.c
+++ b/lib/strcase.c
@@ -259,6 +259,28 @@ bool Curl_safecmp(char *a, char *b)
return !a && !b;
}
+/*
+ * Curl_timestrcmp() returns 0 if the two strings are identical. The time this
+ * function spends is a function of the shortest string, not of the contents.
+ */
+int Curl_timestrcmp(const char *a, const char *b)
+{
+ int match = 0;
+ int i = 0;
+
+ if(a && b) {
+ while(1) {
+ match |= a[i]^b[i];
+ if(!a[i] || !b[i])
+ break;
+ i++;
+ }
+ }
+ else
+ return a || b;
+ return match;
+}
+
/* --- public functions --- */
int curl_strequal(const char *first, const char *second)
--- a/lib/strcase.h
+++ b/lib/strcase.h
@@ -50,5 +50,6 @@ void Curl_strntoupper(char *dest, const
void Curl_strntolower(char *dest, const char *src, size_t n);
bool Curl_safecmp(char *a, char *b);
+int Curl_timestrcmp(const char *first, const char *second);
#endif /* HEADER_CURL_STRCASE_H */
--- a/lib/url.c
+++ b/lib/url.c
@@ -1224,10 +1224,10 @@ ConnectionExists(struct Curl_easy *data,
if(!(needle->handler->flags & PROTOPT_CREDSPERREQUEST)) {
/* This protocol requires credentials per connection,
so verify that we're using the same name and password as well */
- if(strcmp(needle->user, check->user) ||
- strcmp(needle->passwd, check->passwd) ||
- !Curl_safecmp(needle->sasl_authzid, check->sasl_authzid) ||
- !Curl_safecmp(needle->oauth_bearer, check->oauth_bearer)) {
+ if(Curl_timestrcmp(needle->user, check->user) ||
+ Curl_timestrcmp(needle->passwd, check->passwd) ||
+ Curl_timestrcmp(needle->sasl_authzid, check->sasl_authzid) ||
+ Curl_timestrcmp(needle->oauth_bearer, check->oauth_bearer)) {
/* one of them was different */
continue;
}
@@ -1293,8 +1293,8 @@ ConnectionExists(struct Curl_easy *data,
possible. (Especially we must not reuse the same connection if
partway through a handshake!) */
if(wantNTLMhttp) {
- if(strcmp(needle->user, check->user) ||
- strcmp(needle->passwd, check->passwd)) {
+ if(Curl_timestrcmp(needle->user, check->user) ||
+ Curl_timestrcmp(needle->passwd, check->passwd)) {
/* we prefer a credential match, but this is at least a connection
that can be reused and "upgraded" to NTLM */
@@ -1315,8 +1315,10 @@ ConnectionExists(struct Curl_easy *data,
if(!check->http_proxy.user || !check->http_proxy.passwd)
continue;
- if(strcmp(needle->http_proxy.user, check->http_proxy.user) ||
- strcmp(needle->http_proxy.passwd, check->http_proxy.passwd))
+ if(Curl_timestrcmp(needle->http_proxy.user,
+ check->http_proxy.user) ||
+ Curl_timestrcmp(needle->http_proxy.passwd,
+ check->http_proxy.passwd))
continue;
}
else if(check->proxy_ntlm_state != NTLMSTATE_NONE) {
--- a/lib/vauth/digest_sspi.c
+++ b/lib/vauth/digest_sspi.c
@@ -450,8 +450,8 @@ CURLcode Curl_auth_create_digest_http_me
has changed then delete that context. */
if((userp && !digest->user) || (!userp && digest->user) ||
(passwdp && !digest->passwd) || (!passwdp && digest->passwd) ||
- (userp && digest->user && strcmp(userp, digest->user)) ||
- (passwdp && digest->passwd && strcmp(passwdp, digest->passwd))) {
+ (userp && digest->user && Curl_timestrcmp(userp, digest->user)) ||
+ (passwdp && digest->passwd && Curl_timestrcmp(passwdp, digest->passwd))) {
if(digest->http_context) {
s_pSecFn->DeleteSecurityContext(digest->http_context);
Curl_safefree(digest->http_context);
--- a/lib/vtls/vtls.c
+++ b/lib/vtls/vtls.c
@@ -109,8 +109,8 @@ Curl_ssl_config_matches(struct ssl_prima
Curl_safecmp(data->random_file, needle->random_file) &&
Curl_safecmp(data->egdsocket, needle->egdsocket) &&
#ifdef USE_TLS_SRP
- Curl_safecmp(data->username, needle->username) &&
- Curl_safecmp(data->password, needle->password) &&
+ !Curl_timestrcmp(data->username, needle->username) &&
+ !Curl_timestrcmp(data->password, needle->password) &&
(data->authtype == needle->authtype) &&
#endif
Curl_safe_strcasecompare(data->cipher_list, needle->cipher_list) &&
