MFC r309027:
Allocate a struct ifreq rather than using a (wrong) computed size for
the BIOCSETIF ioctl.
The kernel always copies an entire struct ifreq and IPv4 addresses will
always fit in an ifreq.
On systems with pointers larger than 64-bits, the computed size will be
less than the size of struct ifreq, potentially resulting in the kernel
attempting to copyin memory from outside the allocation.
Reviewed by: jhb
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D8445
git-svn-id: svn://svn.freebsd.org/base/stable/9@309305
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