The calculation of the address length for AF_UNIX sockets in the getsockaddrarg function in socketmodule.c returns wrong values on platforms with padded struct sockaddr_un:

*len_ret = len + sizeof(*addr) - sizeof(addr->sun_path);

sizeof(*addr) is for example 112 on an ARM (NSLU2) platforms, while it is 110 on a i386 PC.

The correct way to calculate the length is by directly using the offset of the sun_path field:

*len_ret = len + offsetof(struct sockaddr_un, sun_path);

as suggested in the GNU libc manual:

http://www.gnu.org/software/libc/manual/html_node/Local-Socket-Example.html

The correction also needs to be applied to the makesockaddr function when reversing the above addition in the case of abstract namespace sockets on linux.