netfilter: xtables: Bring SPDX identifier back

Commit e2be04c7f995 ("License cleanup: add SPDX license identifier to
uapi header files with a license") added the correct SPDX identifier to
include/uapi/linux/netfilter/xt_IDLETIMER.h.

A subsequent commit removed it for no reason and reintroduced the UAPI
license incorrectness as the file is now missing the UAPI exception
again.

Add it back and remove the GPLv2 boilerplate while at it.

Fixes: 68983a354a65 ("netfilter: xtables: Add snapshot of hardidletimer target")
Cc: Manoj Basapathi <manojbm@codeaurora.org>
Cc: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

netfilter: xt_IDLETIMER: target v1 - match Android layout

Android has long had an extension to IDLETIMER to send netlink
messages to userspace, see:
https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/include/uapi/linux/netfilter/xt_IDLETIMER.h#42
Note: this is idletimer target rev 1, there is no rev 0 in
the Android common kernel sources, see registration at:
https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/net/netfilter/xt_IDLETIMER.c#483

When we compare that to upstream's new idletimer target rev 1:
https://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next.git/tree/include/uapi/linux/netfilter/xt_IDLETIMER.h#n46

We immediately notice that these two rev 1 structs are the
same size and layout, and that while timer_type and send_nl_msg
are differently named and serve a different purpose, they're
at the same offset.

This makes them impossible to tell apart - and thus one cannot
know in a mixed Android/vanilla environment whether one means
timer_type or send_nl_msg.

Since this is iptables/netfilter uapi it introduces a problem
between iptables (vanilla vs Android) userspace and kernel
(vanilla vs Android) if the two don't match each other.

Additionally when at some point in the future Android picks up
5.7+ it's not at all clear how to resolve the resulting merge
conflict.

Furthermore, since upgrading the kernel on old Android phones
is pretty much impossible there does not seem to be an easy way
out of this predicament.

The only thing I've been able to come up with is some super
disgusting kernel version >= 5.7 check in the iptables binary
to flip between different struct layouts.

By adding a dummy field to the vanilla Linux kernel header file
we can force the two structs to be compatible with each other.

Long term I think I would like to deprecate send_nl_msg out of
Android entirely, but I haven't quite been able to figure out
exactly how we depend on it. It seems to be very similar to
sysfs notifications but with some extra info.

Currently it's actually always enabled whenever Android uses
the IDLETIMER target, so we could also probably entirely
remove it from the uapi in favour of just always enabling it,
but again we can't upgrade old kernels already in the field.

(Also note that this doesn't change the structure's size,
as it is simply fitting into the pre-existing padding, and
that since 5.7 hasn't been released yet, there's still time
to make this uapi visible change)

Cc: Manoj Basapathi <manojbm@codeaurora.org>
Cc: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

netfilter: xtables: Add snapshot of hardidletimer target

This is a snapshot of hardidletimer netfilter target.

This patch implements a hardidletimer Xtables target that can be
used to identify when interfaces have been idle for a certain period
of time.

Timers are identified by labels and are created when a rule is set
with a new label. The rules also take a timeout value (in seconds) as
an option. If more than one rule uses the same timer label, the timer
will be restarted whenever any of the rules get a hit.

One entry for each timer is created in sysfs. This attribute contains
the timer remaining for the timer to expire. The attributes are
located under the xt_idletimer class:

/sys/class/xt_idletimer/timers/<label>

When the timer expires, the target module sends a sysfs notification
to the userspace, which can then decide what to do (eg. disconnect to
save power)

Compared to IDLETIMER, HARDIDLETIMER can send notifications when
CPU is in suspend too, to notify the timer expiry.

v1->v2: Moved all functionality into IDLETIMER module to avoid
code duplication per comment from Florian.

Signed-off-by: Manoj Basapathi <manojbm@codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

License cleanup: add SPDX license identifier to uapi header files with a license

Many user space API headers have licensing information, which is either
incomplete, badly formatted or just a shorthand for referring to the
license under which the file is supposed to be. This makes it hard for
compliance tools to determine the correct license.

Update these files with an SPDX license identifier. The identifier was
chosen based on the license information in the file.

GPL/LGPL licensed headers get the matching GPL/LGPL SPDX license
identifier with the added 'WITH Linux-syscall-note' exception, which is
the officially assigned exception identifier for the kernel syscall
exception:

NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".

This exception makes it possible to include GPL headers into non GPL
code, without confusing license compliance tools.

Headers which have either explicit dual licensing or are just licensed
under a non GPL license are updated with the corresponding SPDX
identifier and the GPLv2 with syscall exception identifier. The format
is:
((GPL-2.0 WITH Linux-syscall-note) OR SPDX-ID-OF-OTHER-LICENSE)

SPDX license identifiers are a legally binding shorthand, which can be
used instead of the full boiler plate text. The update does not remove
existing license information as this has to be done on a case by case
basis and the copyright holders might have to be consulted. This will
happen in a separate step.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne. See the previous patch in this series for the
methodology of how this patch was researched.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

UAPI: (Scripted) Disintegrate include/linux/netfilter

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>