Don't call memcmp with a NULL pointer
If early data is sent to a server, but ALPN is not used then memcmp is
called with a NULL pointer which is undefined behaviour.
Fixes
@@ -1252,8 +1252,9 @@ static int final_early_data(SSL *s, unsigned int context, int sent, int *al)
|| !s->ext.early_data_ok
|| s->hello_retry_request
|| s->s3->alpn_selected_len != s->session->ext.alpn_selected_len
- || memcmp(s->s3->alpn_selected, s->session->ext.alpn_selected,
- s->s3->alpn_selected_len) != 0){
+ || (s->s3->alpn_selected_len > 0
+ && memcmp(s->s3->alpn_selected, s->session->ext.alpn_selected,
+ s->s3->alpn_selected_len) != 0)) {
s->ext.early_data = SSL_EARLY_DATA_REJECTED;
} else {
s->ext.early_data = SSL_EARLY_DATA_ACCEPTED;
