netlink: Make room for the unfinished message when growing the bufferHEADmain

When a message outgrows the writer's buffer, _nlmsg_refill_buffer()
allocates a larger one and moves the unfinished message there.  The new
buffer was sized for the data about to be added alone, so with enough of
the message already written the caller wrote past its end and left it
with datalen > buflen.  A 20-byte message plus an attribute of 8176
bytes got a buffer of 8192 bytes for 8200 bytes of data, and reading it
panicked an INVARIANTS kernel in nl_soreceive().

Size the new buffer for both, and add a ktest for it.

Reviewed by:		glebius
Fixes:			7e5bf68495cc ("netlink: add netlink support")
MFC after:		1 week
Sponsored by:		Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D60541

0 files changed, 0 insertions, 0 deletions