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:
122:cd3f391ac8aa
Parent:
112:f29bb9b99059
Child:
123:06de83222fda
--- a/web.c	Thu May 09 09:58:41 2019 +0000
+++ b/web.c	Sun May 12 17:18:19 2019 +0000
@@ -9,6 +9,13 @@
 
 #define DO_LOGIN DO_SERVER + 0
 
+struct state
+{
+    int      toDo;
+    bool     postComplete;
+    uint32_t delayUntil;
+};
+
 static int decideWhatToDo(char *pPath, char* pLastModified)
 {
     if (HttpSameStr(pPath, "/login")) return DO_LOGIN;
@@ -49,8 +56,12 @@
     if (WebServerThisReply(todo)) return;
 }
 
-static void handleRequest(int size, char* pRequestStream, uint32_t positionInRequestStream, int* pToDo, bool* pPostComplete, uint32_t* pDelayUntil)
+static void handleRequest(int size, char* pRequestStream, uint32_t positionInRequestStream, char* pStateData)
 {
+    struct state* pState = (struct state*)pStateData;
+    
+    pState->delayUntil = MsTimerCount; //Default to no delay unless modified;
+    
     //Handle request for the first packet of data received but leave todo the same after that.
     int contentLength = 0;
     int contentStart  = 0;
@@ -65,48 +76,57 @@
         contentStart = HttpRequestRead(pRequestStream, size, &pMethod, &pPath, &pQuery, &pLastModified, &pCookies, &contentLength);
         
         //Ask the web server what to do
-        *pToDo = decideWhatToDo(pPath, pLastModified);
+        pState->toDo = decideWhatToDo(pPath, pLastModified);
         
         //If what to do is NOTHING, NOT_FOUND or NOT_MODIFIED then no query or post will be valid so stop now
-        if (*pToDo < DO_LOGIN) { *pPostComplete = true; return; }
+        if (pState->toDo < DO_LOGIN) { pState->postComplete = true; return; }
         
         //If what to do is LOGIN then the user has just returned the login form
-        if (*pToDo == DO_LOGIN)
+        if (pState->toDo == DO_LOGIN)
         {
-            handleQuery(*pToDo, pQuery);                  //Read the password and the original location
+            handleQuery(pState->toDo, pQuery);                  //Read the password and the original location
             if (WebLoginQueryPasswordOk)
             {
                 if (!WebLoginSessionIdIsSet())           //If there isn't a session id already
                 {
                     WebLoginSessionIdNew();              //Create a new session id
                 }
-                *pToDo =  WebLoginOriginalToDo;          //Load the original todo and SEND_SESSION_ID
-                *pToDo += DO_SEND_SESSION_ID;
+                pState->toDo =  WebLoginOriginalToDo;          //Load the original todo and SEND_SESSION_ID
+                pState->toDo += DO_SEND_SESSION_ID;
             }
-            *pDelayUntil = MsTimerCount + LOGIN_DELAY_MS; //To prevent brute forcing the hash delay the reply to the login
-            *pPostComplete = true;
+            pState->delayUntil = MsTimerCount + LOGIN_DELAY_MS; //To prevent brute forcing the hash delay the reply to the login
+            pState->postComplete = true;
             return;                                       //Either way no query or post will be valid
         }
         
         //Have a normal request so authenticate
         if (!WebLoginCookiesContainValidSessionId(pCookies))
         {
-            WebLoginOriginalToDo = *pToDo; //Record the original destination for redirection
-            *pToDo = DO_LOGIN;
-            *pPostComplete = true;
+            WebLoginOriginalToDo = pState->toDo; //Record the original destination for redirection
+            pState->toDo = DO_LOGIN;
+            pState->postComplete = true;
             return; //Ignore any query or post as the user is not authenticated
         }
         
         //Handle the query
-        handleQuery(*pToDo, pQuery);
+        handleQuery(pState->toDo, pQuery);
     }
     
     //Do the upload of anything that needs it. Todos it doesn't understand are ignored.
-    if (!*pPostComplete) handlePost(*pToDo, contentLength, contentStart, size, pRequestStream, positionInRequestStream, pPostComplete);
+    if (!pState->postComplete) handlePost(pState->toDo, contentLength, contentStart, size, pRequestStream, positionInRequestStream, &pState->postComplete);
 }
 
-static void sendReply(int todo)
+static int sendReply(char* pStateData)
 {
+    struct state* pState = (struct state*)pStateData;
+    
+    //0: not started; +1: started; -1: wait
+    if (!pState->toDo                       ) return  0; //return not started
+    if (!pState->postComplete               ) return -1; //return started but without adding any data
+    if (!MsTimerAbsolute(pState->delayUntil)) return -1; //return started but without adding any data
+    
+    int todo = pState->toDo; //Make a copy so that we don't modify todo in the state
+
     //Check if todo includes the need to send a cookie
     if (todo >= DO_SEND_SESSION_ID)
     {
@@ -123,6 +143,8 @@
     }
     
     reply(todo);
+    
+    return +1; //return started after adding data
 }
 
 int WebInit()