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bpf: Fix a bpf_kptr_xchg() issue with local kptr #5549

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bpf: Fix a bpf_kptr_xchg() issue with local kptr #5549

wants to merge 2 commits into from

Commits on Aug 21, 2023

  1. bpf: Fix a bpf_kptr_xchg() issue with local kptr 

    When reviewing local percpu kptr support, Alexei discovered a bug
wherea bpf_kptr_xchg() may succeed even if the map value kptr type and
locally allocated obj type do not match ([1]). Missed struct btf_id
comparison is the reason for the bug. This patch added such struct btf_id
comparison and will flag verification failure if types do not match.

  [1] https://lore.kernel.org/bpf/20230819002907.io3iphmnuk43xblu@macbook-pro-8.dhcp.thefacebook.com/#t

Reported-by: Alexei Starovoitov <ast@kernel.org>
Fixes: 738c96d ("bpf: Allow local kptrs to be exchanged via bpf_kptr_xchg")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
    Yonghong Song authored and Kernel Patches Daemon committed Aug 21, 2023
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  2. selftests/bpf: Add a failure test for bpf_kptr_xchg() with local kptr 

    For a bpf_kptr_xchg() with local kptr, if the map value kptr type and
allocated local obj type does not match, with the previous patch,
the below verifier error message will be logged:
  R2 is of type <allocated local obj type> but <map value kptr type> is expected

Without the previous patch, the test will have unexpected success.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
    Yonghong Song authored and Kernel Patches Daemon committed Aug 21, 2023
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