Ifreq ifr_names are incorrect?

Question

The following function determines whether a given string is a valid network device name.

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int isValidNDevice(char *name) { char data[4096]; struct ifconf ifc; struct ifreq *ifr; int sk; int nIntfcs; sk = socket(AF_INET, SOCK_DGRAM, 0); if(sk < 0) { perror("socket"); return 0; } ifc.ifc_len = sizeof(data); ifc.ifc_buf = (caddr_t)data; if(ioctl(sk, SIOCGIFCONF, &ifc) < 0) { perror("ioctl(SIOCGIFCONF)"); return 0; } ifr = (struct ifreq*)data; nIntfcs = ifc.ifc_len / sizeof(struct ifreq); for(int i=0; i < nIntfcs; i++) { safe_printf("%s\n", (&ifr[i])->ifr_name); if (!strcmp((&ifr[i])->ifr_name, name)) { return 1; } } return 0; } 

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When I run this function, I get the following output.

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lo0

stf0

2> S

en1j

0

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This code worked fine a few months ago. What changed? Am I doing something wrong?

OS: OSX El Capitan

Answer 1

The array of structures returned by SIOCGIFCONF IOCTL does not have the same size in OSX. They will have an ifr->ifr_addr.sa_len , which will be different for each structure.

Modified function to take care of this. Hope this helps:

 int isValidNDevice(char *name) { char data[4096]; struct ifconf ifc; struct ifreq *ifr; int sk,length; sk = socket(AF_INET, SOCK_DGRAM, 0); if(sk < 0) { perror("socket"); return 0; } ifc.ifc_len = sizeof(data); ifc.ifc_buf = (caddr_t)data; if(ioctl(sk, SIOCGIFCONF, &ifc) < 0) { perror("ioctl(SIOCGIFCONF)"); return 0; } ifr = (struct ifreq*)data; for(int i=0;i<ifc.ifc_len;) { length=IFNAMSIZ + ifr->ifr_addr.sa_len; printf("%s\n", ifr->ifr_name); if (!strcmp(ifr->ifr_name,name)) { printf("Interface Found!\n"); return 1; } ifr=(struct ifr*)((char*)ifr+length); i+=length; } return 0; }