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Cyril Strejc 9122a70a63 net: multicast: calculate csum of looped-back and forwarded packets 
During a testing of an user-space application which transmits UDP
multicast datagrams and utilizes multicast routing to send the UDP
datagrams out of defined network interfaces, I've found a multicast
router does not fill-in UDP checksum into locally produced, looped-back
and forwarded UDP datagrams, if an original output NIC the datagrams
are sent to has UDP TX checksum offload enabled.

The datagrams are sent malformed out of the NIC the datagrams have been
forwarded to.

It is because:

1. If TX checksum offload is enabled on the output NIC, UDP checksum
   is not calculated by kernel and is not filled into skb data.

2. dev_loopback_xmit(), which is called solely by
   ip_mc_finish_output(), sets skb->ip_summed = CHECKSUM_UNNECESSARY
   unconditionally.

3. Since 35fc92a9 ("[NET]: Allow forwarding of ip_summed except
   CHECKSUM_COMPLETE"), the ip_summed value is preserved during
   forwarding.

4. If ip_summed != CHECKSUM_PARTIAL, checksum is not calculated during
   a packet egress.

The minimum fix in dev_loopback_xmit():

1. Preserves skb->ip_summed CHECKSUM_PARTIAL. This is the
   case when the original output NIC has TX checksum offload enabled.
   The effects are:

     a) If the forwarding destination interface supports TX checksum
        offloading, the NIC driver is responsible to fill-in the
        checksum.

     b) If the forwarding destination interface does NOT support TX
        checksum offloading, checksums are filled-in by kernel before
        skb is submitted to the NIC driver.

     c) For local delivery, checksum validation is skipped as in the
        case of CHECKSUM_UNNECESSARY, thanks to skb_csum_unnecessary().

2. Translates ip_summed CHECKSUM_NONE to CHECKSUM_UNNECESSARY. It
   means, for CHECKSUM_NONE, the behavior is unmodified and is there
   to skip a looped-back packet local delivery checksum validation.

Signed-off-by: Cyril Strejc <cyril.strejc@skoda.cz>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2021-10-26 13:09:22 +01:00
..
acpi Revert "ACPI: Add memory semantics to acpi_os_map_memory()" 2021-09-23 20:39:36 +02:00
asm-generic asm-generic: build fixes for v5.15 2021-10-08 11:57:54 -07:00
clocksource
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-08-30 12:57:10 -07:00
drm
dt-bindings linux-watchdog 5.15-rc1 tag 2021-09-07 13:52:46 -07:00
keys
kunit kunit: fix kernel-doc warnings due to mismatched arg names 2021-10-06 17:54:07 -06:00
kvm KVM: arm64: Fix PMU probe ordering 2021-09-20 12:43:34 +01:00
linux Merge branch 'ucount-fixes-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-10-21 17:27:17 -10:00
math-emu
media
memory
misc
net net: multicast: calculate csum of looped-back and forwarded packets 2021-10-26 13:09:22 +01:00
pcmcia
ras
rdma Merge branch 'sg_nents' into rdma.git for-next 2021-08-30 09:49:59 -03:00
scsi scsi: core: Remove 'current_tag' 2021-09-22 00:13:38 -04:00
soc net: dsa: tag_ocelot_8021q: break circular dependency with ocelot switch lib 2021-10-12 17:35:18 -07:00
sound ALSA: hda: intel: Allow repeatedly probing on codec configuration errors 2021-10-07 09:15:22 +02:00
target scsi: target: Allows backend drivers to fail with specific sense codes 2021-08-17 22:28:40 -04:00
trace block-5.15-2021-10-17 2021-10-17 19:25:20 -10:00
uapi Networking fixes for 5.15-rc7, including fixes from netfilter, and can. 2021-10-21 15:36:50 -10:00
vdso
video
xen xen/privcmd: drop "pages" parameter from xen_remap_pfn() 2021-10-05 08:20:27 +02:00