Question

I want to send a array of data to kernel space , ( i have used call back function in my kext)
problem is when i use send function i see something weird that i explain in 2 scenario:
1)
…
char f[]={‘1′,’2′,’3′,’4′,’5′,’6’};
send (sock,f,sizeof(f),0);
well, when i printf what i receive in kext:
123456

2)
…
// i replace f[2] with 0

char f[]={‘1′,’2’,0,’4′,’5′,’6′};
send (sock,f,sizeof(f),0);

but this time, when i printf what i receive in kext:
120000

it seems that send function make zero every byte after first 0 byte?
what is going on? is this a send function bug?
i used xcode 4.1 and i my os is lion
here is user space part:

int main(int argc, char* const*argv)
{
    struct ctl_info ctl_info;
    struct sockaddr_ctl sc;
    char str[MAX_STRING_LEN];
    int sock = socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL);
    if (sock < 0)
        return -1;
    bzero(&ctl_info, sizeof(struct ctl_info));
    strcpy(ctl_info.ctl_name, "pana.ifmonitor.nke.foo");
    if (ioctl(sock, CTLIOCGINFO, &ctl_info) == -1)
        return -1;
    bzero(&sc, sizeof(struct sockaddr_ctl));
    sc.sc_len = sizeof(struct sockaddr_ctl);
    sc.sc_family = AF_SYSTEM;
    sc.ss_sysaddr = SYSPROTO_CONTROL;
    sc.sc_id = ctl_info.ctl_id;
    sc.sc_unit = 0;
    if (connect(sock, (struct sockaddr *)&sc, sizeof(struct sockaddr_ctl)))
        return -1;


     unsigned char data_send[]={'a','l','i','0','1','2','4','l','i',0,'1','2','4','l','i','0','1'};


    size_t data_recive;
    int j=0;
    char data_rcv[8192];


        send( sock, data_send, 17*sizeof(char), 10 );


        printf("\n");
        sleep(1);


        close(sock);
        return 0;

    }

and this is some part of kernel space code that is responsible for getting user space data:

errno_t EPHandleWrite(kern_ctl_ref ctlref, unsigned int unit, void *userdata,mbuf_t m, int flags)
{

    printf("\n EPHandleWrite called---------------------- \n");
    //char data_rec[50];

    //unsigned char *ptr = (unsigned char*)mbuf_data(m);
    //char ch;
    //mbuf_copydata(m, 0, 50, data_rec);

    //strncpy(&ch, ptr, 1 );


    size_t data_lenght;
    data_lenght = mbuf_pkthdr_len(m);

    char data_receive[data_lenght];
    strncpy( data_receive, ( char * ) mbuf_data(m) , data_lenght );

    printf("data recied %lu\n",data_lenght);

    for(int i=0;i<data_lenght;++i)
    {
        printf("%X ",data_receive[i]);
    }
 return 0
}

well, it print in console:
61 6C 69 30 31 32 34 6C 69 0 0 0 0 0 0 0 0
and when i change send data to:
{'a','l','i','0','1','2','4','l','i',**'0'**,'1','2','4','l','i','0','1'};
i get correct, in fact i get all 0 after first zero byte in send data

Answer 1

The problem is the strncpy line – if you look at the documentation for strncpy, you’ll notice that it only copies until it reaches a 0 byte, so it’s only suitable for dealing with C strings. If you need to copy arbitrary binary data, use memcpy.