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Ido Schimmel 0e4427f8f5 net: loopback: Avoid sending IP packets without an Ethernet header 
After commit 22600596b6 ("ipv4: give an IPv4 dev to blackhole_netdev")
IPv4 neighbors can be constructed on the blackhole net device, but they
are constructed with an output function (neigh_direct_output()) that
simply calls dev_queue_xmit(). The latter will transmit packets via
'skb->dev' which might not be the blackhole net device if dst_dev_put()
switched 'dst->dev' to the blackhole net device while another CPU was
using the dst entry in ip_output(), but after it already initialized
'skb->dev' from 'dst->dev'.

Specifically, the following can happen:

    CPU1                                      CPU2

udp_sendmsg(sk1)                          udp_sendmsg(sk2)
udp_send_skb()                            [...]
ip_output()
    skb->dev = skb_dst(skb)->dev
                                          dst_dev_put()
                                              dst->dev = blackhole_netdev
ip_finish_output2()
    resolves neigh on dst->dev
neigh_output()
neigh_direct_output()
dev_queue_xmit()

This will result in IPv4 packets being sent without an Ethernet header
via a valid net device:

tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on enp9s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
22:07:02.329668 20:00:40:11:18:fb > 45:00:00:44:f4:94, ethertype Unknown
(0x58c6), length 68:
        0x0000:  8dda 74ca f1ae ca6c ca6c 0098 969c 0400  ..t....l.l......
        0x0010:  0000 4730 3f18 6800 0000 0000 0000 9971  ..G0?.h........q
        0x0020:  c4c9 9055 a157 0a70 9ead bf83 38ca ab38  ...U.W.p....8..8
        0x0030:  8add ab96 e052                           .....R

Fix by making sure that neighbors are constructed on top of the
blackhole net device with an output function that simply consumes the
packets, in a similar fashion to dst_discard_out() and
blackhole_netdev_xmit().

Fixes: 8d7017fd62 ("blackhole_netdev: use blackhole_netdev to invalidate dst entries")
Fixes: 22600596b6 ("ipv4: give an IPv4 dev to blackhole_netdev")
Reported-by: Florian Meister <fmei@sfs.com>
Closes: https://lore.kernel.org/netdev/20250210084931.23a5c2e4@hermes.local/
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250220072559.782296-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2025-02-21 16:06:46 -08:00
arch powerpc fixes for 6.14 #3 2025-02-17 10:32:19 -08:00
block block-6.14-20250214 2025-02-14 11:40:59 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Documentation MAINTAINERS: update Nick's contact info 2025-02-17 22:40:04 -08:00
drivers net: loopback: Avoid sending IP packets without an Ethernet header 2025-02-21 16:06:46 -08:00
fs afs: Give an afs_server object a ref on the afs_cell object it points to 2025-02-21 15:06:29 -08:00
include net: better track kernel sockets lifetime 2025-02-21 16:00:58 -08:00
init Kbuild updates for v6.14 2025-01-31 12:07:07 -08:00
io_uring io_uring-6.14-20250214 2025-02-14 11:30:53 -08:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel vfs-6.14-rc4.fixes 2025-02-17 10:38:25 -08:00
lib test_xarray: fix failure in check_pause when CONFIG_XARRAY_MULTI is not defined 2025-02-17 22:40:04 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm kasan: don't call find_vm_area() in a PREEMPT_RT kernel 2025-02-17 22:40:04 -08:00
net net: better track kernel sockets lifetime 2025-02-21 16:00:58 -08:00
rust Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
samples Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
scripts modpost: Fix a few typos in a comment 2025-02-16 03:10:58 +09:00
security Redo of pathname patternization and fix spelling errors. 2025-02-11 10:19:36 -08:00
sound ALSA: seq: Drop UMP events when no UMP-conversion is set 2025-02-17 18:02:02 +01:00
tools Smaller than usual with no fixes from any subtree. 2025-02-20 10:19:54 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt KVM: remove kvm_arch_post_init_vm 2025-02-04 11:27:45 -05:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap mailmap: update Nick's entry 2025-02-17 22:40:03 -08:00
.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 MAINTAINERS: Move Pavel to kernel.org address 2025-02-07 09:12:33 -08:00
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 Smaller than usual with no fixes from any subtree. 2025-02-20 10:19:54 -08:00
Makefile Linux 6.14-rc3 2025-02-16 14:02:44 -08:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.