From 1af9270e908cd50a4f5d815c9b6f794c7d57ed07 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Fri, 25 Sep 2020 23:25:00 +0200 Subject: [PATCH] bpf: disallow attaching modify_return tracing functions to other BPF programs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Toke Høiland-Jørgensen Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index cc9c90d74dc1..52649a5497ce 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11500,6 +11500,11 @@ 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",