Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Kill space at eols.

Fix typo: s/pakcet/packet

-don't pass down, to module's fingerprint function, unused data like
a pointer to the ip header.
-style
-spacing

Prevent the usage of an uninitialized variable: do not accept
StartMediaTx message before an OpnRcvChnAck message was received.

Reviewed by: glebius
Approved by: glebius (mentor)
MFC after: 3 days
Found with: Coverity Prevent(tm)
CID: 498

Summer of Code 2005: improve libalias - part 1 of 2

With the first part of my previous Summer of Code work, we get:

-made libalias modular:

-support for 'particular' protocols (like ftp/irc/etcetc) is no more
hardcoded inside libalias, but it's available through external
modules loadable at runtime

-modules are available both in kernel (/boot/kernel/alias_*.ko) and
user land (/lib/libalias_*)

-protocols/applications modularized are: cuseeme, ftp, irc, nbt, pptp,
skinny and smedia

-added logging support for kernel side

-cleanup

After a buildworld, do a 'mergemaster -i' to install the file libalias.conf
in /etc or manually copy it.

During startup (and after every HUP signal) user land applications running
the new libalias will try to read a file in /etc called libalias.conf:
that file contains the list of modules to load.

User land applications affected by this commit are ppp and natd:
if libalias.conf is present in /etc you won't notice any difference.

The only kernel land bit affected by this commit is ng_nat:
if you are using ng_nat, and it doesn't correctly handle
ftp/irc/etcetc sessions anymore, remember to kldload
the correspondent module (i.e. kldload alias_ftp).

General information and details about the inner working are available
in the libalias man page under the section 'MODULAR ARCHITECTURE
(AND ipfw(4) SUPPORT)'.

NOTA BENE: this commit affects _ONLY_ libalias, ipfw in-kernel nat
support will be part of the next libalias-related commit.

Approved by: glebius
Reviewed by: glebius, ru

Disable checksum processing in LibAlias, when it works as a
kernel module. LibAlias is not aware about checksum offloading,
so the caller should provide checksum calculation. (The only
current consumer is ng_nat(4)). When TCP packet internals has
been changed and it requires checksum recalculation, a cookie
is set in th_x2 field of TCP packet, to inform caller that it
needs to recalculate checksum. This ugly hack would be removed
when LibAlias is made more kernel friendly.

Incremental checksum updates are left as is, since they don't
conflict with offloading.

Approved by: re (scottl)

s/DEBUG/LIBALIAS_DEBUG/, since DEBUG is defined in LINT and
not supported for kernel build.

Always include alias.h before alias_local.h

Play with includes so that libalias can be compiled both as userland
library and kernel module.

Fix a problem in the Skinny ALG where a specially crafted packet could cause
a libalias application (e.g. natd, ppp, etc.) to crash. Note: Skinny support
is not enabled in natd or ppp by default.

Approved by: secteam (nectar)
MFC after: 1 day
Secuiryt: This fixes a remote DoS exploit

Fix Skinny and PPTP NAT'ing after the introduction of the {ip,tcp,udp}_next
functions. Basically, the ip_next() function was used to get the PPTP and
Skinny headers when tcp_next() should have been used instead. Symptoms of
this included a segfault in natd when trying to process a PPTP or Skinny
packet.

Approved by: des

Introduce inline {ip,udp,tcp}_next() functions which take a pointer to an
{ip,udp,tcp} header and return a void * pointing to the payload (i.e. the
first byte past the end of the header and any required padding). Use them
consistently throughout libalias to a) reduce code duplication, b) improve
code legibility, c) get rid of a bunch of alignment warnings.

Make libalias WARNS?=6-clean. This mostly involves renaming variables
named link, foo_link or link_foo to lnk, foo_lnk or lnk_foo, fixing
signed / unsigned comparisons, and shoving unused function arguments
under the carpet.

I was hoping WARNS?=6 might reveal more serious problems, and perhaps
the source of the -O2 breakage, but found no smoking gun.

Parenthesize return values.

Run through indent(1) so I can read the code without getting a headache.
The result isn't quite knf, but it's knfer than the original, and far
more consistent.

Mostly mechanical rework of libalias:

Makes it possible to have multiple packet aliasing instances in a
single process by moving all static and global variables into an
instance structure called "struct libalias".

Redefine a new API based on s/PacketAlias/LibAlias/g

Add new "instance" argument to all functions in the new API.

Implement old API in terms of the new API.

Grrr...add the Skinny alias code forgotten in the last commit.