Andrew Boyson / web

Common stuff for all my devices' web server pages: css, login, log, ipv4, ipv6, firmware update, clock, reset info etc.

Dependents:   oldheating gps motorhome heating

Security

A password has to be set whenever there has been a software reset. Resets following faults or power on do not require a new password as the hash is restored from the RTC GPREG register.

The password is not saved on the device; instead a 32 bit hash of the password is saved. It would take 2^31 attempts to brute force the password: this could be done in under a month if an attempt were possible every millisecond. To prevent this a 200 ms delay is introduced in the reply to the login form, that gives a more reasonable 13 years to brute force the password.

Once the password is accepted a random session id is created. This is 36 bit to give six base 64 characters but without an extra delay. If an attempt could be made every ms then this would still take over a year to brute force.

The most likely attack would to use a dictionary with, say, 10 million entries against the password which would still take 20 days to do.

Diff: web.c

Revision:
125:772948168e4f
Parent:
123:06de83222fda
Child:
127:bd6dd135009d
diff -r a2de6c22f85e -r 772948168e4f web.c
--- a/web.c	Tue May 14 19:19:52 2019 +0000
+++ b/web.c	Fri May 17 15:02:00 2019 +0000
@@ -56,7 +56,7 @@
     if (WebServerThisReply(todo)) return;
 }
 
-static void handleRequest(int size, char* pRequestStream, uint32_t positionInRequestStream, char* pStateData)
+static void handleRequest(char* pStateData, int size, char* pRequestStream, uint32_t positionInRequestStream)
 {
     struct state* pState = (struct state*)pStateData;
     
@@ -116,13 +116,24 @@
     if (!pState->postComplete) handlePost(pState->toDo, contentLength, contentStart, size, pRequestStream, positionInRequestStream, &pState->postComplete);
 }
 
-static bool sendReply(char* pStateData, bool clientFinished)
+static int pollSomethingToSend(char* pStateData, bool clientFinished) //returns 0 no; +1 yes; -1 finished; 
 {
     struct state* pState = (struct state*)pStateData;
     
-    if (!pState->toDo                       ) return clientFinished; //If the client has never sent anything and has finished then finish
-    if (!pState->postComplete               ) return false;
-    if (!MsTimerAbsolute(pState->delayUntil)) return false;
+    if (!pState->toDo)
+    {
+        if (clientFinished) return -1; //The client hasn't requested anything and never will so finish
+        else                return  0; //The client hasn't requested anything yet but still could
+    }
+    if (!pState->postComplete               ) return 0; //Wait for the request (usually a POST) to finish
+    if (!MsTimerAbsolute(pState->delayUntil)) return 0; //Wait a while (usually after a LOGIN attempt)
+    
+    return 1; //Yep, set up anything (just TSL at the moment) then call sendReply
+}
+
+static bool sendReply(char* pStateData)
+{
+    struct state* pState = (struct state*)pStateData;
     
     int todo = pState->toDo; //Make a copy so that we don't modify todo in the state
 
@@ -149,7 +160,8 @@
 int WebInit()
 {
     HttpRequestFunction = handleRequest;
-    HttpReplyPollFunction   = sendReply;
+    HttpPollFunction    = pollSomethingToSend;
+    HttpReplyFunction   = sendReply;
     
     WebLoginInit();