cppcheck/CheckBufferOverrun.cpp

//---------------------------------------------------------------------------
#include "CheckBufferOverrun.h"
#include "tokenize.h"
#include "CommonCheck.h"

#include <sstream>

#include <stdlib.h>     // <- strtoul

//---------------------------------------------------------------------------
extern bool ShowAll;
//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
// Writing dynamic data in buffer without bounds checking
//---------------------------------------------------------------------------

static void _DynamicDataCheck(const TOKEN *ftok, const TOKEN *tok)
{
    const char *var2 = tok->str;
    bool decl = false;
    unsigned int Var2Count = 0;
    for ( const TOKEN *tok2 = ftok; tok2; tok2 = tok2->next )
    {
        if (tok2 == tok)
            break;
        if (match(tok2,"char * var"))
        {
            decl |= (strcmp(getstr(tok2,2),var2)==0);
            tok2 = gettok(tok2,3);
            if ( strcmp(tok2->str, "=") == 0 )
            {
                Var2Count++;
                break;
            }
        }
        if (match(tok2,"char var [ ]"))
        {
            decl |= (strcmp(getstr(tok2,1),var2)==0);
            tok2 = gettok(tok2,3);
        }

        // If ShowAll, only strlen(var2) counts
        if ( ShowAll )
        {
            if (match(tok2,"strlen ( var )") &&
                strcmp(getstr(tok2,2),var2)==0)
            {
                Var2Count++;
                break;
            }
        }

        // If not ShowAll, all usage of "var2" counts
        else
        {
            if (strcmp(tok2->str,var2)==0)
            {
                Var2Count++;
                break;
            }
        }
    }

    // The size of Var2 isn't checked, is it?
    if (decl && Var2Count == 0)
    {
        std::ostringstream ostr;
        ostr << FileLine(tok) << ": A string with unknown length is copied to buffer.";
        ReportErr(ostr.str());
    }
}


static void CheckBufferOverrun_DynamicData()
{
    for (const TOKEN *ftok = FindFunction(tokens,0); ftok; ftok = FindFunction(ftok->next,0))
    {
        int indentlevel = 0;
        for (const TOKEN *tok = ftok; tok; tok = tok->next)
        {
            if (tok->str[0] == '{')
                indentlevel++;
            else if (tok->str[0] == '}')
            {
                indentlevel--;
                if (indentlevel <= 0)
                    break;
            }


            if (match(tok,"strcpy ( var , var )") ||
                match(tok,"strcat ( var , var )") )
            {
                _DynamicDataCheck(ftok,gettok(tok,4));
            }

            if (match(tok,"sprintf ( var"))
            {
                for ( const TOKEN *tok2 = gettok(tok,3); tok2; tok2 = tok2->next )
                {
                    if (tok2->str[0] == ')')
                        break;
                    if (match(tok2,", var ,") || match(tok2,", var )"))
                    {
                        _DynamicDataCheck(ftok,tok2->next);
                    }
                }
            }

        }
    }
}
//---------------------------------------------------------------------------





//---------------------------------------------------------------------------
// Buffer overrun..
//---------------------------------------------------------------------------

static void CheckBufferOverrun_LocalVariable_CheckScope( const TOKEN *tok, const char varname[], const int size, const int total_size )
{
    int indentlevel = 0;
    for ( ; tok; tok = tok->next )
    {
        if (tok->str[0]=='{')
        {
            indentlevel++;
            continue;
        }

        if (tok->str[0]=='}')
        {
            indentlevel--;
            if ( indentlevel < 0 )
                return;
            continue;
        }


        // Array index..
        if (strcmp(tok->str,varname)==0 && match(tok->next,"[ num ]"))
        {
            const char *str = getstr(tok, 2);
            if (strtol(str, NULL, 10) >= size)
            {
                std::ostringstream ostr;
                ostr << FileLine(tok) << ": Array index out of bounds";
                ReportErr(ostr.str());
            }
            continue;
        }


        // memset, memcmp, memcpy, strncpy, fgets..
        if (strcmp(tok->str,"memset")==0 ||
            strcmp(tok->str,"memcpy")==0 ||
            strcmp(tok->str,"memmove")==0 ||
            strcmp(tok->str,"memcmp")==0 ||
            strcmp(tok->str,"strncpy")==0 ||
            strcmp(tok->str,"fgets")==0 )
        {
            if (match(tok->next,"( var , num , num )") ||
                match(tok->next,"( var , var , num )") )
            {
                const char *var1 = getstr(tok, 2);
                const char *var2 = getstr(tok, 4);
                const char *num  = getstr(tok, 6);

                if ( atoi(num)>total_size &&
                     (strcmp(var1,varname)==0 ||
                      strcmp(var2,varname)==0 ) )
                {
                    std::ostringstream ostr;
                    ostr << FileLine(tok) << ": Buffer overrun";
                    ReportErr(ostr.str());
                }
            }
            continue;
        }


        // Loop..
        if ( match(tok, "for (") )
        {
            const TOKEN *tok2 = gettok( tok, 2 );

            // for - setup..
            if ( match(tok2, "var = 0 ;") )
                tok2 = gettok(tok2, 4);
            else if ( match(tok2, "type var = 0 ;") )
                tok2 = gettok(tok2, 5);
            else if ( match(tok2, "type type var = 0 ;") )
                tok2 = gettok(tok2, 6);
            else
                continue;

            // for - condition..
            if ( ! match(tok2, "var < num ;") && ! match(tok2, "var <= num ;"))
                continue;

            // Get index variable and stopsize.
            const char *strindex = tok2->str;
            int value = (tok2->next->str[1] ? 1 : 0) + atoi(getstr(tok2, 2));
            if ( value <= size )
                continue;

            // Goto the end of the for loop..
            while (tok2 && strcmp(tok2->str,")"))
                tok2 = tok2->next;
            if (!gettok(tok2,5))
                break;
            int indentlevel2 = 0;
            while (tok2)
            {
                if ( tok2->str[0] == ';' && indentlevel == 0 )
                    break;

                if ( tok2->str[0] == '{' )
                    indentlevel2++;

                if ( tok2->str[0] == '}' )
                {
                    indentlevel2--;
                    if ( indentlevel2 <= 0 )
                        break;
                }

                if ( match( tok2, "var [ var ]" ) &&
                     strcmp(tok2->str,varname)==0 &&
                     strcmp(getstr(tok2,2),strindex)==0 )
                {
                    std::ostringstream ostr;
                    ostr << FileLine(tok2) << ": Buffer overrun";
                    ReportErr(ostr.str());
                    break;
                }

                tok2 = tok2->next;
            }
            continue;
        }


        // Writing data into array..
        if (match(tok,"strcpy ( var , "))
        {
            int len = 0;
            if (strcmp(getstr(tok, 2), varname) == 0)
            {
                const char *str = getstr(tok, 4);
                if (str[0] == '\"')
                {
                    while (*str)
                    {
                        if (*str=='\\')
                            str++;
                        str++;
                        len++;
                    }
                }
            }
            if (len > 2 && len >= (int)size + 2)
            {
                std::ostringstream ostr;
                ostr << FileLine(tok) << ": Buffer overrun";
                ReportErr(ostr.str());
            }
            continue;
        }


        // Function call..
        // Todo: This is just experimental. It must be more versatile..
        if ( match( tok, "var ( var )" ) && strcmp(varname, getstr(tok,2)) == 0 )
        {
            // Find function..
            const TOKEN *ftok = FindFunction( tokens, tok->str );
            if ( ! ftok )
                continue;

            // Parse head of function..
            while ( ftok )
            {
                if ( match( ftok, "var ) {" ) )
                {
                    CheckBufferOverrun_LocalVariable_CheckScope( gettok(ftok,3), ftok->str, size, total_size );
                    break;
                }

                if ( ftok->str[0] == '{' )
                    break;

                ftok = ftok->next;
            }
        }
    }
}


static void CheckBufferOverrun_LocalVariable()
{
    int indentlevel = 0;
    for (const TOKEN *tok = tokens; tok; tok = tok->next)
    {
        if (tok->str[0]=='{')
            indentlevel++;

        else if (tok->str[0]=='}')
            indentlevel--;

        else if (indentlevel > 0 && match(tok, "type var [ num ] ;"))
        {
            const char *varname = getstr(tok,1);
            unsigned int size = strtoul(getstr(tok,3), NULL, 10);
            int total_size = size * SizeOfType(tok->str);
            if (total_size == 0)
                continue;

            CheckBufferOverrun_LocalVariable_CheckScope( gettok(tok,5), varname, size, total_size );
        }
    }
}
//---------------------------------------------------------------------------

static void CheckBufferOverrun_StructVariable_CheckVar( const TOKEN *tok1, const char varname[], const char arrname[], const int arrsize )
{
    const char *badpattern[] = {"varname",".","arrname","[","","]",NULL};
    badpattern[0] = varname;
    badpattern[2] = arrname;
    const TOKEN *tok2 = findtoken( tok1, badpattern );
    while (tok2)
    {
        if ( IsNumber( getstr(tok2, 4) ) )
        {
            if ( atoi( getstr(tok2, 4) ) >= arrsize )
            {
                std::ostringstream errmsg;
                errmsg << FileLine(tok2) << ": Array index out of bounds";
                ReportErr(errmsg.str());
            }
        }
        tok2 = findtoken( tok2->next, badpattern );
    }
}
//---------------------------------------------------------------------------

static void CheckBufferOverrun_StructVariable()
{
    const char *declstruct_pattern[] = {"struct","","{",0};
    for ( const TOKEN * tok = findtoken( tokens, declstruct_pattern );
          tok;
          tok = findtoken( tok->next, declstruct_pattern ) )
    {
        const char *structname = tok->next->str;

        if ( ! IsName( structname ) )
            continue;

        // Found a struct declaration. Search for arrays..
        for ( TOKEN * tok2 = tok->next->next; tok2; tok2 = tok2->next )
        {
            if ( tok2->str[0] == '}' )
                break;

            if ( strchr( ";{,(", tok2->str[0] ) )
            {
                // Declare array..
                if ( match(tok2->next, "var var [ num ] ;") )
                {
                    const char *arrname = getstr(tok2, 2);
                    const char *arrsize = getstr(tok2, 4);

                    for ( const TOKEN *tok3 = tokens; tok3; tok3 = tok3->next )
                    {
                        if ( strcmp(tok3->str, structname) )
                            continue;

                        // Declare variable: Fred fred1;
                        if ( match( tok3->next, "var ;" ) )
                        {
                            const char *varname = tok3->next->str;
                            CheckBufferOverrun_StructVariable_CheckVar( tok3, varname, arrname, atoi(arrsize) );
                        }

                        // Declare pointer: Fred *fred1
                        else if ( match(tok3->next, "* var") && tok3->next->next->next && strchr(",);=", tok3->next->next->next->str[0]) )
                        {
                            const char *varname = tok3->next->next->str;
                            CheckBufferOverrun_StructVariable_CheckVar( tok3, varname, arrname, atoi(arrsize) );
                        }
                    }
                }
            }
        }
    }
}
//---------------------------------------------------------------------------

void CheckBufferOverrun()
{
    CheckBufferOverrun_DynamicData();
    CheckBufferOverrun_LocalVariable();
    CheckBufferOverrun_StructVariable();
}
//---------------------------------------------------------------------------








//---------------------------------------------------------------------------
// Dangerous functions
//---------------------------------------------------------------------------

void WarningDangerousFunctions()
{
    for (const TOKEN *tok = tokens; tok; tok = tok->next)
    {
        if (match(tok, "gets ("))
        {
            std::ostringstream ostr;
            ostr << FileLine(tok) << ": Found 'gets'. You should use 'fgets' instead";
            ReportErr(ostr.str());
        }

        else if (match(tok, "scanf (") && strcmp(getstr(tok,2),"\"%s\"") == 0)
        {
            std::ostringstream ostr;
            ostr << FileLine(tok) << ": Found 'scanf'. You should use 'fgets' instead";
            ReportErr(ostr.str());
        }
    }
}
//---------------------------------------------------------------------------