UNIX：recv出现内存问题-malloc.c：3096：sYSMALLOc：断言

Question

like in the topic I have a problem with my project for university. I've tried to do it myself for a long time now, but with my full-time work my free time is just not enough.

Error I get:

all: malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed. Aborted

Faulty part of code

void obslugagracza(int sock, int numergracza){
    int wybor, read_size, kto, ile;
    char client_message[1000];
    char message[1000];
    time_t rawtime;
    while(wyscig==0)
    {
        wypisz("Co chcesz zrobic?\n\n1 - Sprawdz ilosc kredytow\n2 - Dodaj kredytow\n3 - Wyplac kredyty\n",sock);
        wypisz("4 - Kto w nastepnym wyscigu?\n5 - Wyniki poprzedniego wyscigu\n6 - Obstaw najblizszy wyscig\n7 - Kiedy wyscig?\n\n", sock);
        while( (read_size = recv(sock , client_message , 100 , 0)) > 0 )
        {
            if(wyscig==1)
                break;
            wybor=atoi(client_message);
            if(wybor==1)
            {
                sprintf(message,"TEMP %i  \n",plist[numergracza].money);
                wypisz(message,sock);
                sleep(4);
            }
            else if(wybor==2)
            {
                wypisz("TEMP", sock);
                read_size = recv(sock , message , maxnamel , 0);
                message[read_size-1]=0;
                plist[numergracza].money+=atoi(message);
                sprintf(message,"TEMP",plist[numergracza].money);
                wypisz(message,sock);
                sleep(4);
            }
            else if(wybor==3)
            {
                wypisz("TEMP", sock);
                read_size = recv(sock , message , maxnamel , 0);
                message[read_size-1]=0;
                if(atoi(message)>plist[numergracza].money)
                    wypisz("TEMP", sock);
                else
                {
                    plist[numergracza].money-=atoi(message);

                    sprintf(message,"TEMP",plist[numergracza].money);
                    wypisz(message,sock);
                }
            }
            else if(wybor==4)
            {
                wypisznastepnych(sock);

            }
            else if(wybor==5)
            {
                if(firstrace==0)
                    wypisz("TEMP", sock);
                else
                {
                    char messaget[100];
                    int i, horsen=8;
                    if (hnumber<horsen)
                        horsen=hnumber;
                    wypisz("TEMP", sock);
                    for(i=0;i<horsen;i++)
                    {
                        if(results[i].inrace==1)
                            sprintf(messaget,"TEMP %s \n", results[i].name);
                        wypisz(messaget,sock);
                    }
                }
            }
            else if(wybor==6)
            {
                wypisznastepnych(sock);
                sleep(3);
                wypisz("TEMP", sock);
                read_size = recv(sock , client_message , maxnamel , 0);
                client_message[read_size-1]=0;
                kto=atoi(client_message);
                wypisz("TEMP", sock);
                read_size = recv(sock , client_message , maxnamel , 0);
                client_message[read_size-1]=0;
                ile=atoi(client_message);
                if(ile>plist[numergracza].money)
                    wypisz("TEMP", sock);
                else
                {
                    plist[numergracza].money-=ile;
                    plist[numergracza].bet+=ile;
                    plist[numergracza].bethorse=kto;
                    sprintf(message,"TEMP",race[kto], ile);
                    wypisz(message,sock);
                }
            }
            else if(wybor==7)
            {
                time( &rawtime);
                sprintf(message,"TEMP",(int)(nextr-rawtime)/60, (int)(nextr-rawtime)%60);
                wypisz(message,sock);
            }
            else
            {
                wypisz("TEMP",sock);
            }
            sleep(3);
            wypisz("Co chcesz zrobic?\n\n1 - Sprawdz ilosc kredytow\n2 - Dodaj kredytow\n3 - Wyplac kredyty\n",sock);
            wypisz("4 - Kto w nastepnym wyscigu?\n5 - Wyniki poprzedniego wyscigu\n6 - Obstaw najblizszy wyscig\n7 - Kiedy wyscig?\n\n", sock);
        }
    }   
}

If I understand correctly, error happens on the second loop of while (client has picked one of options, it works correctly, then menu shows up again, he picks again(doesn'tmatter which option), and error happens.

so error on line

while( (read_size = recv(sock , client_message , 100 , 0)) > 0 )

What may be the source of this issue? on few gorums I've read about memory corruption, but I have no idea how to resolve this.

And small question on the side - is this the proper way to allocate memory?

char *messagew ;
messagew=malloc(sizeof(char)*100+1);

I know code quality sucks, but due to my job and 2nd univeristy, I do this program in parts, often not really remembering where I've stopped and what now. Since program is mostly done, I probably will have more questions after I resolve this one (fixing anything now will probably produce more problems with the amount and quality of code).

Of course all these TEMP messages are only here, to make code shorter - I have normal messages to client, but I doubt they help anything with the problem.

Answer 1

The source is a memory corruption, no doubt arising as a result of some undefined behaviour in your code, probably a buffer overrun . The nature of memory bugs is such that the root cause might be far removed from the point where you are getting the error (to be honest, you are quite lucky to be getting a sensible error message at all).

The easiest way to debug this is probably by running your program through Valgrind .