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UPSTREAM: 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: 18644cec714a ("bpf: Fix use-after-free in fmod_ret check")
Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Change-Id: I4f4d2e4a0464143c87e40f2a67a54f84a206203c
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Toke Høiland-Jørgensen 2020-09-25 23:25:00 +02:00 • committed by basamaryan
commit 98faf62462
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GPG key ID: 210D5384FB2A5885
1 changed files with 5 additions and 0 deletions
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5
kernel/bpf/verifier.c
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@ -11665,6 +11665,11 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
verbose(env, "%s is not sleepable\n",
prog->aux->attach_func_name);
} else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
if (tgt_prog) {
verbose(env, "can't modify return codes of BPF programs\n");
ret = -EINVAL;
goto out;
}
ret = check_attach_modify_return(prog, addr);
if (ret)
verbose(env, "%s() is not modifiable\n",