[NET] compat ifconf: fix limits

A recent change to compat. dev_ifconf() in fs/compat_ioctl.c
causes ifconf data to be truncated 1 entry too early when copying it
to userspace. The correct amount of data (length) is returned,
but the final entry is empty (zero, not filled in).
The for-loop 'i' check should use <= to allow the final struct
ifreq32 to be copied. I also used the ifconf-corruption program
in kernel bugzilla #4746 to make sure that this change does not
re-introduce the corruption.

Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

fs/compat_ioctl.c

···
 	ifr = ifc.ifc_req;
 	ifr32 = compat_ptr(ifc32.ifcbuf);
 	for (i = 0, j = 0;
-             i + sizeof (struct ifreq32) < ifc32.ifc_len && j < ifc.ifc_len;
+             i + sizeof (struct ifreq32) <= ifc32.ifc_len && j < ifc.ifc_len;
 	     i += sizeof (struct ifreq32), j += sizeof (struct ifreq)) {
 		if (copy_in_user(ifr32, ifr, sizeof (struct ifreq32)))
 			return -EFAULT;