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Keep track of whether mbedtls_ssl_set_hostname() has been called

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Use a special marker as ssl->hostname if mbedtls_ssl_set_hostname() has been
called with NULL. If mbedtls_ssl_set_hostname() has never been called, the
field is NULL, as before.

No behavior change apart from now emitting a different log message depending
on whether mbedtls_ssl_set_hostname() has been called with NULL or not at all.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2025-02-12 23:53:25 +01:00
parent 520ceb2726
commit f33c45f84d
3 changed files with 55 additions and 20 deletions
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29
library/ssl_tls.c
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@ -40,6 +40,12 @@
#if defined(MBEDTLS_X509_CRT_PARSE_C)
/* A magic value for `ssl->hostname` indicating that
* mbedtls_ssl_set_hostname() has been called with `NULL`.
* If mbedtls_ssl_set_hostname() has never been called on `ssl`, then
* `ssl->hostname == NULL`. */
static const char *const ssl_hostname_skip_cn_verification = "";
#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/** Whether mbedtls_ssl_set_hostname() has been called.
*
@ -52,11 +58,6 @@
static int mbedtls_ssl_has_set_hostname_been_called(
const mbedtls_ssl_context *ssl)
{
/* We can't tell the difference between the case where
* mbedtls_ssl_set_hostname() has not been called at all, and
* the case where it was last called with NULL. For the time
* being, we assume the latter, i.e. we behave as if there had
* been an implicit call to mbedtls_ssl_set_hostname(ssl, NULL). */
return ssl->hostname != NULL;
}
#endif
@ -68,12 +69,16 @@ static
#endif
const char *mbedtls_ssl_get_hostname_pointer(const mbedtls_ssl_context *ssl)
{
if (ssl->hostname == ssl_hostname_skip_cn_verification) {
return NULL;
}
return ssl->hostname;
}
static void mbedtls_ssl_free_hostname(mbedtls_ssl_context *ssl)
{
if (ssl->hostname != NULL) {
if (ssl->hostname != NULL &&
ssl->hostname != ssl_hostname_skip_cn_verification) {
mbedtls_platform_zeroize(ssl->hostname, strlen(ssl->hostname));
mbedtls_free(ssl->hostname);
}
@ -99,13 +104,19 @@ int mbedtls_ssl_set_hostname(mbedtls_ssl_context *ssl, const char *hostname)
* so we can free it safely */
mbedtls_ssl_free_hostname(ssl);
/* Passing NULL as hostname shall clear the old one */
if (hostname == NULL) {
ssl->hostname = NULL;
/* Passing NULL as hostname clears the old one, but leaves a
* special marker to indicate that mbedtls_ssl_set_hostname()
* has been called. */
/* ssl->hostname should be const, but isn't. We won't actually
* write to the buffer, so it's ok to cast away the const. */
ssl->hostname = (char *) ssl_hostname_skip_cn_verification;
} else {
ssl->hostname = mbedtls_calloc(1, hostname_len + 1);
if (ssl->hostname == NULL) {
/* mbedtls_ssl_set_hostname() has been called, but unsuccessfully.
* Leave ssl->hostname in the same state as if the function had
* not been called, i.e. a null pointer. */
return MBEDTLS_ERR_SSL_ALLOC_FAILED;
}