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[bpf-next,v8,01/11] bpf: disallow attaching modify_return tracing functions to other BPF programs

Message ID 160079991486.8301.10483022567832542496.stgit@toke.dk
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series bpf: Support multi-attach for freplace programs | expand

Commit Message

Toke Høiland-Jørgensen Sept. 22, 2020, 6:38 p.m. UTC 
From: Toke Høiland-Jørgensen <toke@redhat.com>

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 <toke@redhat.com>
---
 kernel/bpf/verifier.c |    5 +++++
 1 file changed, 5 insertions(+)

Comments

Andrii Nakryiko Sept. 23, 2020, 5:25 p.m. UTC | #1 
On Tue, Sep 22, 2020 at 11:39 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@redhat.com>
>
> 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 <toke@redhat.com>
> ---

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  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",
>
diff mbox series

Patch

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",