Impossible de changer l'adresse IP en utilisant ioctl SIOCSIFADDR

Question

J'essaye d'écrire un programme c pour changer l'adresse IP et le masque de sous-réseau d'une interface réseau. Cependant, l'appel à ioctl avec la commande SIOCSIFADDR renvoie toujours EINVAL. Mon code de programme est le suivant.

/* inet_config.c */ 

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <unistd.h> 
#include <fcntl.h> 
#include <errno.h> 
#include <sys/types.h> 
#include <sys/ioctl.h> 
#include <sys/socket.h> 
#include <netdb.h> 
#include <net/if.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 

#define _INTERFACE_NAME argv[1] 
#define _INET_ADDRESS argv[2] 
#define _SUBNET_MASK  argv[3] 

int main(int argc, char ** argv) { 
    int sockfd, inet_addr_config_result, subnet_mask_config_result, ioctl_result; 
    struct ifreq ifr; 
    struct sockaddr_in *inet_addr, *subnet_mask; 

    /* Prepare the struct ifreq */ 

    bzero(ifr.ifr_name, IFNAMSIZ); 
    bzero((char *)&(ifr.ifr_addr), sizeof(struct sockaddr)); 
    bzero((char *)&(ifr.ifr_netmask), sizeof(struct sockaddr)); 

    strcpy(ifr.ifr_name, _INTERFACE_NAME); 

    ifr.ifr_addr.sa_family = AF_INET; 
    inet_addr = (struct sockaddr_in *)&(ifr.ifr_addr); 
    inet_addr_config_result = inet_pton(AF_INET, _INET_ADDRESS, &(inet_addr->sin_addr)); 

    ifr.ifr_netmask.sa_family = AF_INET; 
    subnet_mask = (struct sockaddr_in *)&(ifr.ifr_netmask); 
    subnet_mask_config_result = inet_pton(AF_INET, _SUBNET_MASK, &(subnet_mask->sin_addr)); 

    /* Error handling */ 

    if(inet_addr_config_result == 0) 
    { 
    fprintf(stderr, "%s: inet_pton: Invalid IPv4 address.\n", argv[0]); 
    exit(EXIT_FAILURE); 
    } 

    if(inet_addr_config_result < 0) 
    { 
    fprintf(stderr, "%s: inet_pton: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    if(subnet_mask_config_result == 0) 
    { 
    fprintf(stderr, "%s: inet_pton: Invalid IPv4 subnet mask.\n", argv[0]); 
    exit(EXIT_FAILURE); 
    } 

    if(subnet_mask_config_result < 0) 
    { 
    fprintf(stderr, "%s: inet_pton: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    /* Open socket for ioctl calls */ 

    sockfd = socket(AF_INET, SOCK_DGRAM, 0); 
    if(sockfd < 0) 
    { 
    fprintf(stderr, "%s: socket: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    /* Call ioctl to configure network devices */ 

    ioctl_result = ioctl(sockfd, SIOCSIFADDR, &ifr); // Set IP address 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCSIFADDR: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    ioctl_result = ioctl(sockfd, SIOCSIFNETMASK, &ifr); // Set subnet mask 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCSIFNETMASK: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    ioctl_result = ioctl(sockfd, SIOCGIFFLAGS, &ifr); 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCGIFFLAGS: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    ifr.ifr_flags |= (IFF_UP | IFF_RUNNING); 

    ioctl(sockfd, SIOCSIFFLAGS, &ifr); 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCSIFFLAGS: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    printf("Network device configured\n"); 

    return 0; 
} 

En tapant la commande

./inet_config wlp2s0 192.168.2.0 255.255.255.0 

je reçois le message d'erreur suivant:

./inet_config: ioctl SIOCSIFADDR: Invalid argument 

(inet_config est le nom du binaire compilé à partir du code ci-dessus et wlp2s0 est mon WiFi interface.)

Answer 1

Votre problème provient du ifr variable: Il est composé d'un union, donc ifr_addr et ifr_netmask pointent vers la même zone de mémoire:

struct ifreq { 
    char ifr_name[IFNAMSIZ]; /* Interface name */ 
    union { // <-- all your problem comes from this union 
     struct sockaddr ifr_addr; 
     struct sockaddr ifr_dstaddr; 
     struct sockaddr ifr_broadaddr; 
     struct sockaddr ifr_netmask; 
     struct sockaddr ifr_hwaddr; 
     short   ifr_flags; 
     int    ifr_ifindex; 
     int    ifr_metric; 
     int    ifr_mtu; 
     struct ifmap ifr_map; 
     char   ifr_slave[IFNAMSIZ]; 
     char   ifr_newname[IFNAMSIZ]; 
     char   *ifr_data; 
    }; 
}; 

Votre code peut fonctionner avec une correction: l'adresse et le masque sont stockées dans deux sockaddr_in structures qui sont reproduites dans ifr juste avant de l'utiliser.

/* inet_config.c */ 
[...] 

int main(int argc, char ** argv) { 
    int sockfd, inet_addr_config_result, subnet_mask_config_result, ioctl_result; 
    struct ifreq ifr; 
    /// note: no pointer here 
    struct sockaddr_in inet_addr, subnet_mask; 

    /* Prepare the struct ifreq */ 

    bzero(ifr.ifr_name, IFNAMSIZ); 
    strcpy(ifr.ifr_name, _INTERFACE_NAME); 

    /// note: prepare the two struct sockaddr_in 
    inet_addr.sin_family = AF_INET; 
    inet_addr_config_result = inet_pton(AF_INET, _INET_ADDRESS, &(inet_addr.sin_addr)); 

    subnet_mask.sin_family = AF_INET; 
    subnet_mask_config_result = inet_pton(AF_INET, _SUBNET_MASK, &(subnet_mask.sin_addr)); 

    /* Error handling */ 
    [...] 
    /* Open socket for ioctl calls */ 

    sockfd = socket(AF_INET, SOCK_DGRAM, 0); 
    if(sockfd < 0) 
    { 
    fprintf(stderr, "%s: socket: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    /* Call ioctl to configure network devices */ 

    /// put addr in ifr structure 
    memcpy(&(ifr.ifr_addr), &inet_addr, sizeof (struct sockaddr)); 
    ioctl_result = ioctl(sockfd, SIOCSIFADDR, &ifr); // Set IP address 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCSIFADDR: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    /// put mask in ifr structure 
    memcpy(&(ifr.ifr_addr), &subnet_mask, sizeof (struct sockaddr)); 
    ioctl_result = ioctl(sockfd, SIOCSIFNETMASK, &ifr); // Set subnet mask 
    if(ioctl_result < 0) 
    { 
    fprintf(stderr, "%s: ioctl SIOCSIFNETMASK: ", argv[0]); 
    perror(""); 
    exit(EXIT_FAILURE); 
    } 

    [....] 

    printf("Network device configured\n"); 

    return 0; 
}