[PATCH v4 bpf 0/2] bpf: return proper error codes for lwt redirect

[Yan Zhai <yan@cloudflare.com>]

lwt xmit hook does not expect positive return values in function
ip_finish_output2 and ip6_finish_output2. However, BPF redirect programs
can return positive values such like NET_XMIT_DROP, NET_RX_DROP, and etc
as errors. Such return values can panic the kernel unexpectedly:

https://gist.github.com/zhaiyan920/8fbac245b261fe316a7ef04c9b1eba48

This patch fixes the return values from BPF redirect, so the error
handling would be consistent at xmit hook. It also adds a few test cases
to prevent future regressions.

v3: https://lore.kernel.org/bpf/cover.1690255889.git.yan@cloudflare.com/ 
v2: https://lore.kernel.org/netdev/ZLdY6JkWRccunvu0@debian.debian/ 
v1: https://lore.kernel.org/bpf/ZLbYdpWC8zt9EJtq@debian.debian/

changes since v3:
  * minor change in commit message and changelogs
  * tested by Jakub Sitnicki

changes since v2:
  * subject name changed
  * also covered redirect to ingress case
  * added selftests

changes since v1:
  * minor code style changes

Yan Zhai (2):
  bpf: fix skb_do_redirect return values
  bpf: selftests: add lwt redirect regression test cases

 include/linux/netdevice.h                     |   2 +
 net/core/filter.c                             |   9 +-
 tools/testing/selftests/bpf/Makefile          |   1 +
 .../selftests/bpf/progs/test_lwt_redirect.c   |  66 +++++++
 .../selftests/bpf/test_lwt_redirect.sh        | 174 ++++++++++++++++++
 5 files changed, 250 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_lwt_redirect.c
 create mode 100755 tools/testing/selftests/bpf/test_lwt_redirect.sh

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2.30.2