[PATCH net 0/9] net/sched: Fix packet loops in mirred and netem

[Jamal Hadi Salim <jhs@mojatatu.com>]

This patchset adds a 2-bit per-skb tc_depth counter that travels with
the packet to help  fixes packet loops caused by mirred ingress
redirects and netem duplication in stacked qdisc trees.
The existing per-CPU mirred nest tracking loses state when a packet is
deferred through the backlog or moves between CPUs via XPS/RPS.
A per-skb field covers both cases.

Patch 1 adds the tc_depth field in a padding hole in sk_buff.
Patches 2-3 revert the check_netem_in_tree() fix and its tests,
which broke legitimate multi-netem configurations.
Patch 4 uses tc_depth to stop netem duplicate recursion.
Patch 5 uses tc_depth to catch mirred ingress redirect loops.
Patch 6 fixes the infinite loop in the mirred egress blockcast case.
Patch 7 fixes an skb leak in early return error scenarios in tcf_mirred_act
for redirect (caught by Sashiko [1]).
Patches 8-9 add mirred and netem test cases.

Changes in v4:
- Provide better context in patch 1 commit to appease Sashiko
  We'll see if it will stop yapping about corner cases! I believe
  I am making history being the first human to talk directly to Sashiko
  in a patch submission;->
- Fix infinite loop for the mirred egress blockcast case (patch 6)
- Fix skb leak in tcf_mirred_act caught by Sashiko (patch 7)

Changes in v3:
- Renamed skb->ttl to skb->tc_depth to avoid confusion with IP TTL
- Expanded commit messages
- Split mirred and netem test cases into separate patches
- No code changes from v2

Changes in v2:
- Do not reuse skb->from_ingress (which was moved to skb->cb)

[1] https://sashiko.dev/#/patchset/20260413082027.2244884-1-hxzene%40gmail.com

Jamal Hadi Salim (5):
  net: Introduce skb tc depth field to track packet loops
  net/sched: Revert "net/sched: Restrict conditions for adding
    duplicating netems to qdisc tree"
  Revert "selftests/tc-testing: Add tests for restrictions on netem
    duplication"
  net/sched: fix packet loop on netem when duplicate is on
  net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop

Kito Xu (veritas501) (1):
  net/sched: act_mirred: Fix blockcast recursion bypass leading to stack
    overflow

Victor Nogueira (3):
  net/sched: act_mirred: Fix skb leak in early mirred redirect returns
  selftests/tc-testing: Add mirred test cases exercising loops
  selftests/tc-testing: Add netem test case exercising loops

 include/linux/skbuff.h                        |   2 +
 net/sched/act_mirred.c                        |  67 +-
 net/sched/sch_netem.c                         |  47 +-
 .../tc-testing/tc-tests/actions/mirred.json   | 616 +++++++++++++++++-
 .../tc-testing/tc-tests/infra/qdiscs.json     |   5 +-
 .../tc-testing/tc-tests/qdiscs/netem.json     |  96 +--
 6 files changed, 691 insertions(+), 142 deletions(-)

-- 
2.34.1