Messages in this thread | | | Subject | Re: [PATCH v2] xdp: Sample xdp program implementing ip forward | From | David Daney <> | Date | Tue, 10 Oct 2017 14:37:51 -0700 |
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On 10/10/2017 10:19 AM, Stephen Hemminger wrote: > On Tue, 10 Oct 2017 12:58:52 +0530 > Christina Jacob <christina.jacob.koikara@gmail.com> wrote: > >> +/* Get the mac address of the interface given interface name */ >> +static long *getmac(char *iface) >> +{ >> + int fd; >> + struct ifreq ifr; >> + long *mac = NULL; >> + >> + fd = socket(AF_INET, SOCK_DGRAM, 0); >> + ifr.ifr_addr.sa_family = AF_INET; >> + strncpy(ifr.ifr_name, iface, IFNAMSIZ - 1); >> + ioctl(fd, SIOCGIFHWADDR, &ifr); >> + mac = (long *)ifr.ifr_hwaddr.sa_data; >> + close(fd); >> + return mac; > > Always check return value of ioctl. > You are assuming sizeof(long) > 6 bytes. > Also the byte order.
Also:
Returning the address of a local variable (ifr.ifr_hwaddr.sa_data), and then dereferencing it outside of the function is not correct.
The casting of the char sa_data[] to a long * may cause alignment faults on some architectures. The may also be endinaness issues depending on how the data are manipulated if you pack all those chars into a long.
If we think that a MAC address is char[6], then it may be best to define the data structures as such and manipulate it as an array instead of trying to pack it into a long.
Keep working on this though, this program will surely be useful.
David Daney
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