EAP-pwd server: Fix last fragment length validation

All but the last fragment had their length checked against the remaining
room in the reassembly buffer. This allowed a suitably constructed last
fragment frame to try to add extra data that would go beyond the buffer.
The length validation code in wpabuf_put_data() prevents an actual
buffer write overflow from occurring, but this results in process
termination. (CVE-2015-5314)

Signed-off-by: Jouni Malinen <j@w1.fi>

diff --git a/src/eap_server/eap_server_pwd.c b/src/eap_server/eap_server_pwd.c
index cb83ff7305bd0644656d421261ba3a2ea40671df..9f787ab32592d840dd07c757285df6a2bd14f18d 100644 (file)
--- a/src/eap_server/eap_server_pwd.c
+++ b/src/eap_server/eap_server_pwd.c
@@ -970,7 +970,7 @@ static void eap_pwd_process(struct eap_sm *sm, void *priv,
        /*
         * the first and all intermediate fragments have the M bit set
         */
-       if (EAP_PWD_GET_MORE_BIT(lm_exch)) {
+       if (EAP_PWD_GET_MORE_BIT(lm_exch) || data->in_frag_pos) {
                if ((data->in_frag_pos + len) > wpabuf_size(data->inbuf)) {
                        wpa_printf(MSG_DEBUG, "EAP-pwd: Buffer overflow "
                                   "attack detected! (%d+%d > %d)",
@@ -981,6 +981,8 @@ static void eap_pwd_process(struct eap_sm *sm, void *priv,
                }
                wpabuf_put_data(data->inbuf, pos, len);
                data->in_frag_pos += len;
+       }
+       if (EAP_PWD_GET_MORE_BIT(lm_exch)) {
                wpa_printf(MSG_DEBUG, "EAP-pwd: Got a %d byte fragment",
                           (int) len);
                return;
@@ -990,8 +992,6 @@ static void eap_pwd_process(struct eap_sm *sm, void *priv,
         * buffering fragments so that's how we know it's the last)
         */
        if (data->in_frag_pos) {
-               wpabuf_put_data(data->inbuf, pos, len);
-               data->in_frag_pos += len;
                pos = wpabuf_head_u8(data->inbuf);
                len = data->in_frag_pos;
                wpa_printf(MSG_DEBUG, "EAP-pwd: Last fragment, %d bytes",