client: fix GUI RPC password generation bug on Win

Apparently when Win runs in a VM, the random number generation functions
(e.g. CryptGenRandom()) don't work.
We weren't checking for this, resulting in a garbage (and guessable) password.

Also change function names to indicate that string is not just random,
but also hard to guess.

client/gui_rpc_server.cpp

@@ -142,17 +142,7 @@ void GUI_RPC_CONN_SET::get_password() {
 
     // if no password file, make a random password
     //
-    retval = make_random_string(password);
-    if (retval) {
-        if (cc_config.os_random_only) {
-            msg_printf(
-                NULL, MSG_INTERNAL_ERROR,
-                "OS random string generation failed, exiting"
-            );
-            exit(1);
-        }
-        gstate.host_info.make_random_string("guirpc", password);
-    }
+    make_secure_random_string(password);
 
     // try to write it to the file.
     // if fail, just return

client/gui_rpc_server_ops.cpp

@@ -1377,7 +1377,7 @@ void handle_get_auth_id(MIOFILE& fout) {
     AUTH_INFO ai;
     ai.id = id++;
     ai.seqno = 0;
-    make_random_string(ai.salt);
+    make_secure_random_string(ai.salt);
     auth_infos.push_back(ai);
     fout.printf("<auth_id>%d</auth_id>\n<auth_salt>%s</auth_salt>\n", ai.id, ai.salt);
 }

client/hostinfo_network.cpp

@@ -53,6 +53,7 @@
 #include "util.h"
 
 #include "client_msgs.h"
+#include "client_state.h"
 
 #include "hostinfo.h"
 
@@ -119,6 +120,20 @@ void HOST_INFO::make_random_string(const char* salt, char* out) {
     md5_block((const unsigned char*) buf, (int)strlen(buf), out);
 }
 
+void make_secure_random_string(char* out) {
+    int retval = make_secure_random_string_os(out);
+    if (retval) {
+        if (cc_config.os_random_only) {
+            msg_printf(
+                NULL, MSG_INTERNAL_ERROR,
+                "OS random string generation failed, exiting"
+            );
+            exit(1);
+        }
+        gstate.host_info.make_random_string("guirpc", out);
+    }
+}
+
 // make a host cross-project ID.
 // Should be unique across hosts with very high probability
 //

client/main.cpp

@@ -192,8 +192,8 @@ static void init_core_client(int argc, char** argv) {
 #ifdef _WIN32
     if (!cc_config.allow_multiple_clients && !gstate.cmdline_dir) {
         chdir_to_data_dir();
-#endif
     }
+#endif
 
 #ifndef _WIN32
     if (g_use_sandbox)

lib/hostinfo.h

@@ -104,7 +104,10 @@ public:
 
     bool host_is_running_on_batteries();
 #ifdef __APPLE__
-    bool users_idle(bool check_all_logins, double idle_time_to_run, double *actual_idle_time=NULL);
+    bool users_idle(
+        bool check_all_logins, double idle_time_to_run,
+        double *actual_idle_time=NULL
+    );
 #else
     bool users_idle(bool check_all_logins, double idle_time_to_run);
 #endif
@@ -120,14 +123,26 @@ public:
     void clear_host_info();
     void make_random_string(const char* salt, char* out);
     void generate_host_cpid();
-    static bool parse_linux_os_info(FILE* file, const LINUX_OS_INFO_PARSER parser,
-        char* os_name, const int os_name_size, char* os_version, const int os_version_size);
-    static bool parse_linux_os_info(const std::string& line, const LINUX_OS_INFO_PARSER parser,
-        char* os_name, const int os_name_size, char* os_version, const int os_version_size);
-    static bool parse_linux_os_info(const std::vector<std::string>& lines, const LINUX_OS_INFO_PARSER parser,
-        char* os_name, const int os_name_size, char* os_version, const int os_version_size);
+    static bool parse_linux_os_info(
+        FILE* file, const LINUX_OS_INFO_PARSER parser,
+        char* os_name, const int os_name_size, char* os_version,
+        const int os_version_size
+    );
+    static bool parse_linux_os_info(
+        const std::string& line, const LINUX_OS_INFO_PARSER parser,
+        char* os_name, const int os_name_size, char* os_version,
+        const int os_version_size
+    );
+    static bool parse_linux_os_info(
+        const std::vector<std::string>& lines,
+        const LINUX_OS_INFO_PARSER parser,
+        char* os_name, const int os_name_size, char* os_version,
+        const int os_version_size
+    );
 };
 
+extern void make_secure_random_string(char*);
+
 #ifdef _WIN64
 int get_wsl_information(bool& wsl_available, WSLS& wsls);
 #endif

lib/md5_file.cpp

@@ -125,10 +125,10 @@ std::string md5_string(const unsigned char* data, int nbytes) {
     return std::string(output);
 }
 
-// make a random 32-char string
-// (the MD5 of some quasi-random bits)
+// make a secure (i.e. hard to guess)
+// 32-char string using OS-supplied random bits
 //
-int make_random_string(char* out) {
+int make_secure_random_string_os(char* out) {
     char buf[256];
 #ifdef _WIN32
     HCRYPTPROV hCryptProv;
@@ -144,9 +144,7 @@ int make_random_string(char* out) {
         
     CryptReleaseContext(hCryptProv, 0);
 #elif defined ANDROID
-    // /dev/random not available on Android, using stdlib function instead
-    int i = rand();
-    snprintf(buf, sizeof(buf), "%d", i);
+    return -1;
 #else
 #ifndef _USING_FCGI_
     FILE* f = fopen("/dev/random", "r");

lib/md5_file.h

@@ -41,5 +41,5 @@ inline std::string md5_string(std::string const& data) {
     return md5_string((const unsigned char*) data.c_str(), (int)data.size());
 }
 
-extern int make_random_string(char*);
+extern int make_secure_random_string_os(char*);
 #endif