cmsg_len is supposed to be socklen_t according to standards, but it was made
size_t on Linux, see BZ 16919. For ports that have it socklen_t, SIZE_MAX is
too large. We can however explicitly cast it to the type of cmsg_len so it
will fit according to that type.
The inline and library functions that the CMSG_NXTHDR macro may expand
to increment the pointer to the header before checking the stride of
the increment against available space. Since C only allows incrementing
pointers to one past the end of an array, the increment must be done
after a length check. This commit fixes that and includes a regression
test for CMSG_FIRSTHDR and CMSG_NXTHDR.
The Linux, Hurd, and generic headers are all changed.
Tested on Linux on armv7hl, i686, x86_64, aarch64, ppc64le, and s390x.
[BZ #28846]
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
