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From: Hao Luo <haoluo@google.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
	Shakeel Butt <shakeelb@google.com>,
	Joe Burton <jevburton.kernel@gmail.com>,
	Tejun Heo <tj@kernel.org>,
	joshdon@google.com, sdf@google.com, bpf@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall
Date: Tue, 15 Mar 2022 12:47:54 -0700	[thread overview]
Message-ID: <CA+khW7h=Ykav0c=vZQTMeVumxgNwq-pRgko1VTk4wjzCVnxHFA@mail.gmail.com> (raw)
In-Reply-To: <YjDiQbam/P+KkgKE@zeniv-ca.linux.org.uk>

On Tue, Mar 15, 2022 at 12:02 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Tue, Mar 15, 2022 at 10:27:39AM -0700, Hao Luo wrote:
>
> > Option 1: We can put restrictions on the pathname passed into this
> > helper. We can explicitly require the parameter dirfd to be in bpffs
> > (we can verify). In addition, we check pathname to be not containing
> > any dot or dotdot, so the resolved path will end up inside bpffs,
> > therefore won't take ->i_rwsem that is in the callchain of
> > cgroup_mkdir().
>
> Won't be enough - mount --bind the parent under itself and there you go...
> Sure, you could prohibit mountpoint crossing, etc., but at that point
> I'd question the usefulness of pathname resolution in the first place.

[Apologies for resend, my response did not get delivered to mail list]

I don't see a use case where we need to bind mount the directories in
bpffs, right now. So in option 1, we can also prohibit mountpoint
crossing.

Pathname resolution is still useful in this case. Imagine we want to
put all the created dirs under a base dir, we can open the base dir
and reuse its fd for multiple mkdirs, for example:

Userspace:
  fd = openat(..., "/sys/fs/bpf", ...);
  pass fd to the bpf prog

bpf prog:
  bpf_mkdirat(fd, "common1", ...);
  bpf_mkdirat(fd, "common1/a", ...);
  bpf_mkdirat(fd, "common1/b", ...);
  bpf_mkdirat(fd, "common2", ...);
  ...

It would be very inconvenient if we can't resolve multi-level paths.

As Alexei said, another option is to delegate syscall to a worker
thread. IMHO, we could do that in future if we find there is a need
for the full feature of pathname resolution.

Al, does that sound good?

  reply	other threads:[~2022-03-15 19:48 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-25 23:43 [PATCH bpf-next v1 0/9] Extend cgroup interface with bpf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall Hao Luo
2022-02-27  5:18   ` Kumar Kartikeya Dwivedi
2022-02-28 22:10     ` Hao Luo
2022-03-02 19:34       ` Alexei Starovoitov
2022-03-03 18:50         ` Hao Luo
2022-03-04 18:37           ` Hao Luo
2022-03-05 23:47             ` Alexei Starovoitov
2022-03-08 21:08               ` Hao Luo
2022-03-02 20:55   ` Yonghong Song
2022-03-03 18:56     ` Hao Luo
2022-03-03 19:13       ` Yonghong Song
2022-03-03 19:15         ` Hao Luo
2022-03-12  3:46   ` Al Viro
2022-03-14 17:07     ` Hao Luo
2022-03-14 23:10       ` Al Viro
2022-03-15 17:27         ` Hao Luo
2022-03-15 18:59           ` Alexei Starovoitov
2022-03-15 19:03             ` Alexei Starovoitov
2022-03-15 19:00           ` Al Viro
2022-03-15 19:47             ` Hao Luo [this message]
2022-02-25 23:43 ` [PATCH bpf-next v1 2/9] bpf: Add BPF_OBJ_PIN and BPF_OBJ_GET in the bpf_sys_bpf helper Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 3/9] selftests/bpf: tests mkdir, rmdir, unlink and pin in syscall Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints Hao Luo
2022-03-02 19:41   ` Alexei Starovoitov
2022-03-03 19:37     ` Hao Luo
2022-03-03 19:59       ` Alexei Starovoitov
2022-03-02 21:23   ` Yonghong Song
2022-03-02 21:30     ` Alexei Starovoitov
2022-03-03  1:08       ` Yonghong Song
2022-03-03  2:29         ` Alexei Starovoitov
2022-03-03 19:43           ` Hao Luo
2022-03-03 20:02             ` Alexei Starovoitov
2022-03-03 20:04               ` Alexei Starovoitov
2022-03-03 22:06                 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 5/9] cgroup: Sleepable cgroup tracepoints Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 6/9] libbpf: Add sleepable tp_btf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 7/9] bpf: Lift permission check in __sys_bpf when called from kernel Hao Luo
2022-03-02 20:01   ` Alexei Starovoitov
2022-03-03 19:14     ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter Hao Luo
2022-02-26  2:32   ` kernel test robot
2022-02-26  2:32   ` kernel test robot
2022-02-26  2:53   ` kernel test robot
2022-03-02 21:59   ` Yonghong Song
2022-03-03 20:02     ` Hao Luo
2022-03-02 22:45   ` Kumar Kartikeya Dwivedi
2022-03-03  2:03     ` Yonghong Song
2022-03-03  3:03       ` Kumar Kartikeya Dwivedi
2022-03-03  4:00         ` Alexei Starovoitov
2022-03-03  7:33         ` Yonghong Song
2022-03-03  8:13           ` Kumar Kartikeya Dwivedi
2022-03-03 21:52           ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 9/9] selftests/bpf: Tests using sleepable tracepoints to monitor cgroup events Hao Luo

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