wireguard: allowedips: free empty intermediate nodes when removing single node

When removing single nodes, it's possible that that node's parent is an
empty intermediate node, in which case, it too should be removed.
Otherwise the trie fills up and never is fully emptied, leading to
gradual memory leaks over time for tries that are modified often. There
was originally code to do this, but was removed during refactoring in
2016 and never reworked. Now that we have proper parent pointers from
the previous commits, we can implement this properly.

In order to reduce branching and expensive comparisons, we want to keep
the double pointer for parent assignment (which lets us easily chain up
to the root), but we still need to actually get the parent's base
address. So encode the bit number into the last two bits of the pointer,
and pack and unpack it as needed. This is a little bit clumsy but is the
fastest and less memory wasteful of the compromises. Note that we align
the root struct here to a minimum of 4, because it's embedded into a
larger struct, and we're relying on having the bottom two bits for our
flag, which would only be 16-bit aligned on m68k.

The existing macro-based helpers were a bit unwieldy for adding the bit
packing to, so this commit replaces them with safer and clearer ordinary
functions.

We add a test to the randomized/fuzzer part of the selftests, to free
the randomized tries by-peer, refuzz it, and repeat, until it's supposed
to be empty, and then then see if that actually resulted in the whole
thing being emptied. That combined with kmemcheck should hopefully make
sure this commit is doing what it should. Along the way this resulted in
various other cleanups of the tests and fixes for recent graphviz.

Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Cc: stable@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

wireguard: allowedips: allocate nodes in kmem_cache

The previous commit moved from O(n) to O(1) for removal, but in the
process introduced an additional pointer member to a struct that
increased the size from 60 to 68 bytes, putting nodes in the 128-byte
slab. With deployed systems having as many as 2 million nodes, this
represents a significant doubling in memory usage (128 MiB -> 256 MiB).
Fix this by using our own kmem_cache, that's sized exactly right. This
also makes wireguard's memory usage more transparent in tools like
slabtop and /proc/slabinfo.

Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

wireguard: allowedips: remove nodes in O(1)

Previously, deleting peers would require traversing the entire trie in
order to rebalance nodes and safely free them. This meant that removing
1000 peers from a trie with a half million nodes would take an extremely
long time, during which we're holding the rtnl lock. Large-scale users
were reporting 200ms latencies added to the networking stack as a whole
every time their userspace software would queue up significant removals.
That's a serious situation.

This commit fixes that by maintaining a double pointer to the parent's
bit pointer for each node, and then using the already existing node list
belonging to each peer to go directly to the node, fix up its pointers,
and free it with RCU. This means removal is O(1) instead of O(n), and we
don't use gobs of stack.

The removal algorithm has the same downside as the code that it fixes:
it won't collapse needlessly long runs of fillers. We can enhance that
in the future if it ever becomes a problem. This commit documents that
limitation with a TODO comment in code, a small but meaningful
improvement over the prior situation.

Currently the biggest flaw, which the next commit addresses, is that
because this increases the node size on 64-bit machines from 60 bytes to
68 bytes. 60 rounds up to 64, but 68 rounds up to 128. So we wind up
using twice as much memory per node, because of power-of-two
allocations, which is a big bummer. We'll need to figure something out
there.

Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Cc: stable@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: WireGuard secure network tunnel

WireGuard is a layer 3 secure networking tunnel made specifically for
the kernel, that aims to be much simpler and easier to audit than IPsec.
Extensive documentation and description of the protocol and
considerations, along with formal proofs of the cryptography, are
available at:

* https://www.wireguard.com/
* https://www.wireguard.com/papers/wireguard.pdf

This commit implements WireGuard as a simple network device driver,
accessible in the usual RTNL way used by virtual network drivers. It
makes use of the udp_tunnel APIs, GRO, GSO, NAPI, and the usual set of
networking subsystem APIs. It has a somewhat novel multicore queueing
system designed for maximum throughput and minimal latency of encryption
operations, but it is implemented modestly using workqueues and NAPI.
Configuration is done via generic Netlink, and following a review from
the Netlink maintainer a year ago, several high profile userspace tools
have already implemented the API.

This commit also comes with several different tests, both in-kernel
tests and out-of-kernel tests based on network namespaces, taking profit
of the fact that sockets used by WireGuard intentionally stay in the
namespace the WireGuard interface was originally created, exactly like
the semantics of userspace tun devices. See wireguard.com/netns/ for
pictures and examples.

The source code is fairly short, but rather than combining everything
into a single file, WireGuard is developed as cleanly separable files,
making auditing and comprehension easier. Things are laid out as
follows:

* noise.[ch], cookie.[ch], messages.h: These implement the bulk of the
cryptographic aspects of the protocol, and are mostly data-only in
nature, taking in buffers of bytes and spitting out buffers of
bytes. They also handle reference counting for their various shared
pieces of data, like keys and key lists.

* ratelimiter.[ch]: Used as an integral part of cookie.[ch] for
ratelimiting certain types of cryptographic operations in accordance
with particular WireGuard semantics.

* allowedips.[ch], peerlookup.[ch]: The main lookup structures of
WireGuard, the former being trie-like with particular semantics, an
integral part of the design of the protocol, and the latter just
being nice helper functions around the various hashtables we use.

* device.[ch]: Implementation of functions for the netdevice and for
rtnl, responsible for maintaining the life of a given interface and
wiring it up to the rest of WireGuard.

* peer.[ch]: Each interface has a list of peers, with helper functions
available here for creation, destruction, and reference counting.

* socket.[ch]: Implementation of functions related to udp_socket and
the general set of kernel socket APIs, for sending and receiving
ciphertext UDP packets, and taking care of WireGuard-specific sticky
socket routing semantics for the automatic roaming.

* netlink.[ch]: Userspace API entry point for configuring WireGuard
peers and devices. The API has been implemented by several userspace
tools and network management utility, and the WireGuard project
distributes the basic wg(8) tool.

* queueing.[ch]: Shared function on the rx and tx path for handling
the various queues used in the multicore algorithms.

* send.c: Handles encrypting outgoing packets in parallel on
multiple cores, before sending them in order on a single core, via
workqueues and ring buffers. Also handles sending handshake and cookie
messages as part of the protocol, in parallel.

* receive.c: Handles decrypting incoming packets in parallel on
multiple cores, before passing them off in order to be ingested via
the rest of the networking subsystem with GRO via the typical NAPI
poll function. Also handles receiving handshake and cookie messages
as part of the protocol, in parallel.

* timers.[ch]: Uses the timer wheel to implement protocol particular
event timeouts, and gives a set of very simple event-driven entry
point functions for callers.

* main.c, version.h: Initialization and deinitialization of the module.

* selftest/*.h: Runtime unit tests for some of the most security
sensitive functions.

* tools/testing/selftests/wireguard/netns.sh: Aforementioned testing
script using network namespaces.

This commit aims to be as self-contained as possible, implementing
WireGuard as a standalone module not needing much special handling or
coordination from the network subsystem. I expect for future
optimizations to the network stack to positively improve WireGuard, and
vice-versa, but for the time being, this exists as intentionally
standalone.

We introduce a menu option for CONFIG_WIREGUARD, as well as providing a
verbose debug log and self-tests via CONFIG_WIREGUARD_DEBUG.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: David Miller <davem@davemloft.net>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>