From: Johannes Berg <johan...@sipsolutions.net>
Date: Sat, 26 Jan 2019 21:12:19 +0100
> From: Johannes Berg <johannes.b...@intel.com>
>
> Digging through the ioctls with Al because of the previous
> patches, we found that on 64-bit decnet's dn_dev_ioctl()
> is wrong, because struct ifreq::ifr_ifru is actually 24
> bytes (not 16 as expected from struct sockaddr) due to the
> ifru_map and ifru_settings members.
>
> Clearly, decnet expects the ioctl to be called with a struct
> like
> struct ifreq_dn {
> char ifr_name[IFNAMSIZ];
> struct sockaddr_dn ifr_addr;
> };
>
> since it does
> struct ifreq *ifr = ...;
> struct sockaddr_dn *sdn = (struct sockaddr_dn *)&ifr->ifr_addr;
>
> This means that DN_IFREQ_SIZE is too big for what it wants on
> 64-bit, as it is
> sizeof(struct ifreq) - sizeof(struct sockaddr) +
> sizeof(struct sockaddr_dn)
>
> This assumes that sizeof(struct sockaddr) is the size of ifr_ifru
> but that isn't true.
>
> Fix this to use offsetof(struct ifreq, ifr_ifru).
>
> This indeed doesn't really matter much - the result is that we
> copy in/out 8 bytes more than we should on 64-bit platforms. In
> case the "struct ifreq_dn" lands just on the end of a page though
> it might lead to faults.
>
> As far as I can tell, it has been like this forever, so it seems
> very likely that nobody cares.
>
> Signed-off-by: Johannes Berg <johannes.b...@intel.com>
Applied.
