[PATCH bpf v2 0/2] Fix bpf_skb_load_bytes_relative for cgroup_skb/egress

[YiFei Zhu <zhuyifei1999@gmail.com>]

When cgroup_skb/egress triggers the MAC header is not set. On the other hand,
load_bytes_relative unconditionally calls skb_mac_header which, when MC not
set, returns a pointer after the tail pointer, breaking the logic even if the
caller requested the NET header.

Fix is to conditionally use skb_mac_header or skb_network_header depending on
the requested header, -EFAULT when the header is not set. Added a test that
asserts during cgroup_skb/egress request for MAC header returns -EFAULT and
request for NET header succeeds.

Updates since v1:
* Reverted the bound condition check to account for bad offset parameter
  larger than data length.
* Add test asssertion for failure return code on the condition above.

YiFei Zhu (2):
  net/filter: Permit reading NET in load_bytes_relative when MAC not set
  selftests/bpf: Add cgroup_skb/egress test for load_bytes_relative

 net/core/filter.c                             | 16 +++--
 .../bpf/prog_tests/load_bytes_relative.c      | 71 +++++++++++++++++++
 .../selftests/bpf/progs/load_bytes_relative.c | 48 +++++++++++++
 3 files changed, 128 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/load_bytes_relative.c
 create mode 100644 tools/testing/selftests/bpf/progs/load_bytes_relative.c

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2.27.0