mbedtls_ssl_decrypt_buf(): fix buffer overread with stream cipher
With stream ciphers, add a check that there's enough room to read a MAC in
the record. Without this check, subtracting the MAC length from the data
length resulted in an integer underflow, causing the MAC calculation to try
reading (SIZE_MAX + 1 - maclen) bytes of input, which is a buffer overread.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index c8ffc1e..2726cbc 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -1546,8 +1546,16 @@
#if defined(MBEDTLS_SSL_SOME_SUITES_USE_STREAM)
if (ssl_mode == MBEDTLS_SSL_MODE_STREAM) {
+ if (rec->data_len < transform->maclen) {
+ MBEDTLS_SSL_DEBUG_MSG(1,
+ ("Record too short for MAC:"
+ " %" MBEDTLS_PRINTF_SIZET " < %" MBEDTLS_PRINTF_SIZET,
+ rec->data_len, transform->maclen));
+ return MBEDTLS_ERR_SSL_INVALID_MAC;
+ }
+
/* The only supported stream cipher is "NULL",
- * so there's nothing to do here.*/
+ * so there's no encryption to do here.*/
} else
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_STREAM */
#if defined(MBEDTLS_GCM_C) || \
@@ -2010,7 +2018,7 @@
unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD] = { 0 };
unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD] = { 0 };
- /* If the initial value of padlen was such that
+ /* For CBC+MAC, If the initial value of padlen was such that
* data_len < maclen + padlen + 1, then padlen
* got reset to 1, and the initial check
* data_len >= minlen + maclen + 1
@@ -2022,6 +2030,9 @@
* subtracted either padlen + 1 (if the padding was correct)
* or 0 (if the padding was incorrect) since then,
* hence data_len >= maclen in any case.
+ *
+ * For stream ciphers, we checked above that
+ * data_len >= maclen.
*/
rec->data_len -= transform->maclen;
ssl_extract_add_data_from_record(add_data, &add_data_len, rec,