Re: [PATCH bpf-next v8 01/11] bpf: disallow attaching modify_return tracing functions to other BPF programs
From: Andrii Nakryiko <hidden>
Date: 2020-09-23 17:25:47
Also in:
bpf
On Tue, Sep 22, 2020 at 11:39 AM Toke Høiland-Jørgensen [off-list ref] wrote:
From: Toke Høiland-Jørgensen <redacted>
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")
Signed-off-by: Toke Høiland-Jørgensen <redacted>
---Acked-by: Andrii Nakryiko <redacted>
quoted hunk ↗ jump to hunk
kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 15ab889b0a3f..797e2b0d8bc2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c@@ -11471,6 +11471,11 @@ 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",