linux-kernel - Re: [PATCH bpf-next v7 4/5] bpf: Make fs kfuncs available for SYSCALL program type

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Message-ID: <CAADnVQLk6w+AkpoWERoid54xZh_FeiV0q1_sVU2o-oMBkP2Y7w@mail.gmail.com>
Date: Tue, 21 Jan 2025 16:43:59 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Juntong Deng <juntong.deng@...look.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Kumar Kartikeya Dwivedi <memxor@...il.com>, snorcht@...il.com, 
	Christian Brauner <brauner@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v7 4/5] bpf: Make fs kfuncs available for SYSCALL
 program type

On Tue, Jan 21, 2025 at 5:09 AM Juntong Deng <juntong.deng@...look.com> wrote:
>
> Currently fs kfuncs are only available for LSM program type, but fs
> kfuncs are generic and useful for scenarios other than LSM.
>
> This patch makes fs kfuncs available for SYSCALL program type.
>
> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> ---
>  fs/bpf_fs_kfuncs.c                                 | 14 ++++++--------
>  .../selftests/bpf/progs/verifier_vfs_reject.c      | 10 ----------
>  2 files changed, 6 insertions(+), 18 deletions(-)
>
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 4a810046dcf3..8a7e9ed371de 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -26,8 +26,6 @@ __bpf_kfunc_start_defs();
>   * acquired by this BPF kfunc will result in the BPF program being rejected by
>   * the BPF verifier.
>   *
> - * This BPF kfunc may only be called from BPF LSM programs.
> - *
>   * Internally, this BPF kfunc leans on get_task_exe_file(), such that calling
>   * bpf_get_task_exe_file() would be analogous to calling get_task_exe_file()
>   * directly in kernel context.
> @@ -49,8 +47,6 @@ __bpf_kfunc struct file *bpf_get_task_exe_file(struct task_struct *task)
>   * passed to this BPF kfunc. Attempting to pass an unreferenced file pointer, or
>   * any other arbitrary pointer for that matter, will result in the BPF program
>   * being rejected by the BPF verifier.
> - *
> - * This BPF kfunc may only be called from BPF LSM programs.
>   */
>  __bpf_kfunc void bpf_put_file(struct file *file)
>  {
> @@ -70,8 +66,6 @@ __bpf_kfunc void bpf_put_file(struct file *file)
>   * reference, or else the BPF program will be outright rejected by the BPF
>   * verifier.
>   *
> - * This BPF kfunc may only be called from BPF LSM programs.
> - *
>   * Return: A positive integer corresponding to the length of the resolved
>   * pathname in *buf*, including the NUL termination character. On error, a
>   * negative integer is returned.
> @@ -184,7 +178,8 @@ BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
>  static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
>  {
>         if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) ||
> -           prog->type == BPF_PROG_TYPE_LSM)
> +           prog->type == BPF_PROG_TYPE_LSM ||
> +           prog->type == BPF_PROG_TYPE_SYSCALL)
>                 return 0;
>         return -EACCES;
>  }
> @@ -197,7 +192,10 @@ static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
>
>  static int __init bpf_fs_kfuncs_init(void)
>  {
> -       return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set);
> +       int ret;
> +
> +       ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set);
> +       return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_fs_kfunc_set);
>  }
>
>  late_initcall(bpf_fs_kfuncs_init);
> diff --git a/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c
> index d6d3f4fcb24c..5aab75fd2fa5 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c
> @@ -148,14 +148,4 @@ int BPF_PROG(path_d_path_kfunc_invalid_buf_sz, struct file *file)
>         return 0;
>  }
>
> -SEC("fentry/vfs_open")
> -__failure __msg("calling kernel function bpf_path_d_path is not allowed")
> -int BPF_PROG(path_d_path_kfunc_non_lsm, struct path *path, struct file *f)
> -{
> -       /* Calling bpf_path_d_path() from a non-LSM BPF program isn't permitted.
> -        */
> -       bpf_path_d_path(path, buf, sizeof(buf));
> -       return 0;
> -}

A leftover from previous versions?
This test should still be rejected by the verifier.