diff mbox series

[bpf-next,v7,01/10] bpf: disallow attaching modify_return tracing functions to other BPF programs

Message ID 160051618391.58048.12525358750568883938.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. 19, 2020, 11:49 a.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 |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Andrii Nakryiko Sept. 21, 2020, 10:39 p.m. UTC | #1 
On Sat, Sep 19, 2020 at 4:50 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>
> ---
>  kernel/bpf/verifier.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 4161b6c406bc..cb1b0f9fd770 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -11442,7 +11442,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>                                         prog->aux->attach_func_name);
>                 } else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
>                         ret = check_attach_modify_return(prog, addr);
> -                       if (ret)
> +                       if (ret || tgt_prog)

can you please do it as a separate check with a more appropriate and
meaningful message?

>                                 verbose(env, "%s() is not modifiable\n",
>                                         prog->aux->attach_func_name);
>                 }
>
Toke Høiland-Jørgensen Sept. 22, 2020, 9:52 a.m. UTC | #2 
Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Sat, Sep 19, 2020 at 4:50 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>
>> ---
>>  kernel/bpf/verifier.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 4161b6c406bc..cb1b0f9fd770 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -11442,7 +11442,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>>                                         prog->aux->attach_func_name);
>>                 } else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
>>                         ret = check_attach_modify_return(prog, addr);
>> -                       if (ret)
>> +                       if (ret || tgt_prog)
>
> can you please do it as a separate check with a more appropriate and
> meaningful message?

Heh, okay, maybe I was being a bit too lazy here ;)

-Toke
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4161b6c406bc..cb1b0f9fd770 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11442,7 +11442,7 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 					prog->aux->attach_func_name);
 		} else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
 			ret = check_attach_modify_return(prog, addr);
-			if (ret)
+			if (ret || tgt_prog)
 				verbose(env, "%s() is not modifiable\n",
 					prog->aux->attach_func_name);
 		}