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.

http/httprequest.c

Committer:
andrewboyson
Date:
2019-09-24
Revision:
130:9a5b8fe308f1

File content as of revision 130:9a5b8fe308f1:

#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include "http.h"
#include "log.h"

static char* terminateThisAndGetNextLine(char* p, char* pE) //Terminates this line and returns the start of the next line or NULL if none
{
    while (true)
    {
        if ( p == pE)   { *p = 0; return NULL;  } //no more buffer - relies on having designed the buffer to be bigger than an ethernet packet
        if (*p == 0)              return NULL;    //there are no more lines
        if (*p == '\n') { *p = 0; return p + 1; } //return the start of the next line
        if (*p < ' ')     *p = 0;                 //terminate the line at any invalid characters but keep going to find the start of the next line
        if (*p >= 0x7f)   *p = 0;                 //terminate the line at any invalid characters but keep going to find the start of the next line
        p++;
    }
}

static void splitRequest(char* p, char** ppMethod, char** ppPath, char** ppQuery)
{        
    *ppMethod   = NULL;
    *ppPath     = NULL;
    *ppQuery    = NULL;

    while (*p == ' ')         //Move past any leading spaces
    {
        if (*p == 0) return;
        p++;
    }
    *ppMethod = p;            //Record the start of the method (GET or POST)
 
    while (*p != ' ')         //Move past the method
    {
        if (*p == 0) return;
        p++;
    } 
    *p = 0;                   //Terminate the method
    p++;                      //Start at next character

    while (*p == ' ')         //Move past any spaces
    {
        if (*p == 0) return;
        p++;
    } 
    *ppPath = p;              //Record the start of the path
    
    while (*p != ' ')         //Move past the path and query
    {
        if (*p == 0) return;
        if (*p == '?')
        {
            *p = 0;           //Terminate the path
            *ppQuery = p + 1; //Record the start of the query
        }
        p++;
    }
    *p = 0;                   //Terminate the path or query
}
static void splitHeader(char* p, char** ppName, char** ppValue)
{
    *ppName    = p;                     //Record the start of the name
    *ppValue   = NULL;

    while (*p != ':')                   //Loop to an ':'
    {
        if (!*p) return;
        p++;
    }
    *p = 0;                             //Terminate the name by replacing the ':' with a NUL char
    p++;
    while (*p == ' ')                   //Move past any spaces
    {
        if (*p == 0) return;
        p++;
    }
    *ppValue = p;                       //Record the start of the value
}
int HttpRequestRead(char *pData, int len, char** ppMethod, char** ppPath, char** ppQuery, char** ppLastModified, char** ppCookies, int* pContentLength)
{
    char* pEnd = pData + len;
    char* pThis = pData;
    char* pNext = terminateThisAndGetNextLine(pThis, pEnd);
    splitRequest(pThis, ppMethod, ppPath, ppQuery);

    *ppLastModified = NULL; //Return NULL if no 'If-Modified-Since' line
    *ppCookies      = NULL; //Return NULL if no 'Cookie'            line
    *pContentLength = 0;    //Return 0    if no 'Content-Length'    line
    while(pNext)
    {
        pThis = pNext;
        pNext = terminateThisAndGetNextLine(pThis, pEnd);
        if (*pThis == 0) break;     //This line is empty ie no more headers
        char* pName;
        char* pValue;
        splitHeader(pThis, &pName, &pValue);
        if (HttpSameStrCaseInsensitive(pName, "If-Modified-Since")) *ppLastModified = pValue;
        if (HttpSameStrCaseInsensitive(pName, "Cookie"           )) *ppCookies      = pValue;
        if (HttpSameStrCaseInsensitive(pName, "Content-Length"   )) *pContentLength = atoi(pValue);
    }
    if (pNext) return pNext - pData;
    else       return len;
}