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Florian Westphal 80cd0487f6 netfilter: bridge: confirm multicast packets before passing them up the stack 
[ Upstream commit 62e7151ae3 ]

conntrack nf_confirm logic cannot handle cloned skbs referencing
the same nf_conn entry, which will happen for multicast (broadcast)
frames on bridges.

 Example:
    macvlan0
       |
      br0
     /  \
  ethX    ethY

 ethX (or Y) receives a L2 multicast or broadcast packet containing
 an IP packet, flow is not yet in conntrack table.

 1. skb passes through bridge and fake-ip (br_netfilter)Prerouting.
    -> skb->_nfct now references a unconfirmed entry
 2. skb is broad/mcast packet. bridge now passes clones out on each bridge
    interface.
 3. skb gets passed up the stack.
 4. In macvlan case, macvlan driver retains clone(s) of the mcast skb
    and schedules a work queue to send them out on the lower devices.

    The clone skb->_nfct is not a copy, it is the same entry as the
    original skb.  The macvlan rx handler then returns RX_HANDLER_PASS.
 5. Normal conntrack hooks (in NF_INET_LOCAL_IN) confirm the orig skb.

The Macvlan broadcast worker and normal confirm path will race.

This race will not happen if step 2 already confirmed a clone. In that
case later steps perform skb_clone() with skb->_nfct already confirmed (in
hash table).  This works fine.

But such confirmation won't happen when eb/ip/nftables rules dropped the
packets before they reached the nf_confirm step in postrouting.

Pablo points out that nf_conntrack_bridge doesn't allow use of stateful
nat, so we can safely discard the nf_conn entry and let inet call
conntrack again.

This doesn't work for bridge netfilter: skb could have a nat
transformation. Also bridge nf prevents re-invocation of inet prerouting
via 'sabotage_in' hook.

Work around this problem by explicit confirmation of the entry at LOCAL_IN
time, before upper layer has a chance to clone the unconfirmed entry.

The downside is that this disables NAT and conntrack helpers.

Alternative fix would be to add locking to all code parts that deal with
unconfirmed packets, but even if that could be done in a sane way this
opens up other problems, for example:

-m physdev --physdev-out eth0 -j SNAT --snat-to 1.2.3.4
-m physdev --physdev-out eth1 -j SNAT --snat-to 1.2.3.5

For multicast case, only one of such conflicting mappings will be
created, conntrack only handles 1:1 NAT mappings.

Users should set create a setup that explicitly marks such traffic
NOTRACK (conntrack bypass) to avoid this, but we cannot auto-bypass
them, ruleset might have accept rules for untracked traffic already,
so user-visible behaviour would change.

Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217777
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-03-06 14:48:36 +00:00
arch s390: use the correct count for __iowrite64_copy() 2024-03-01 13:35:08 +01:00
block block: Fix WARNING in _copy_from_iter 2024-03-01 13:34:49 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: algif_hash - Remove bogus SGL free on zero-length error path 2024-02-23 09:25:11 +01:00
Documentation docs: Instruct LaTeX to cope with deeper nesting 2024-03-01 13:34:58 +01:00
drivers Bluetooth: qca: Fix triggering coredump implementation 2024-03-06 14:48:36 +00:00
fs ksmbd: fix wrong allocation size update in smb2_open() 2024-03-06 14:48:34 +00:00
include netfilter: bridge: confirm multicast packets before passing them up the stack 2024-03-06 14:48:36 +00:00
init update workarounds for gcc "asm goto" issue 2024-02-23 09:24:47 +01:00
io_uring io_uring/net: fix multishot accept overflow handling 2024-02-23 09:25:10 +01:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel 2024-03-01 13:35:07 +01:00
lib netlink: add nla be16/32 types to minlen array 2024-03-06 14:48:34 +00:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: zswap: fix missing folio cleanup in writeback race path 2024-03-01 13:35:10 +01:00
net netfilter: bridge: confirm multicast packets before passing them up the stack 2024-03-06 14:48:36 +00:00
rust rust: upgrade to Rust 1.73.0 2024-02-16 19:10:43 +01:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
scripts bpf, scripts: Correct GPL license name 2024-03-01 13:35:06 +01:00
security lsm: fix the logic in security_inode_getsecctx() 2024-02-23 09:25:02 +01:00
sound ASoC: cs35l34: Fix GPIO name and drop legacy include 2024-03-06 14:48:34 +00:00
tools selftests: mptcp: add mptcp_lib_get_counter 2024-03-01 13:35:11 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add Catherine as xfs maintainer for 6.6.y 2024-02-16 19:10:43 +01:00
Makefile Linux 6.6.20 2024-03-02 18:23:09 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.