bpf: disallow attaching modify_return tracing functions to other BPF programs

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From the checks and commit messages for modify_return, it seems it was
never the intention that it should be possible to attach a tracing program
with expected_attach_type == BPF_MODIFY_RETURN to another BPF program.
However, check_attach_modify_return() will only look at the function name,
so if the target function starts with "security_", the attach will be
allowed even for bpf2bpf attachment.

Fix this oversight by also blocking the modification if a target program is
supplied.

Fixes: 18644cec71 ("bpf: Fix use-after-free in fmod_ret check")
Fixes: 6ba43b761c ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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Toke Høiland-Jørgensen 2020-09-25 23:25:00 +02:00 • committed by Alexei Starovoitov

parent 84a20d8e87

commit 1af9270e90

1 changed files with 5 additions and 0 deletions

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kernel/bpf/verifier.c

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