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Message-ID:
<AM6PR03MB50804F40EA53A4EF22E4FEC999E12@AM6PR03MB5080.eurprd03.prod.outlook.com>
Date: Wed, 22 Jan 2025 21:20:08 +0000
From: Juntong Deng <juntong.deng@...look.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.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 2025/1/22 17:59, Alexei Starovoitov wrote:
> On Wed, Jan 22, 2025 at 5:34 AM Juntong Deng <juntong.deng@...look.com> wrote:
>>
>> On 2025/1/22 00:43, Alexei Starovoitov wrote:
>>> 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.
>>
>> Thanks for your reply.
>>
>> Not a leftover.
>>
>> bpf_path_d_path can be called from SYSCALL program type, not only LSM
>> program type, so it seems a bit weird to keep this test case?
>
> How is it weird?
> How is this related to syscall prog?
> It's a check that fentry prog cannot call it.
Sorry, I misunderstood this test case.
This test case is used to test the filtering for aliases.
I will keep it in the next version.
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