linux-kernel - Re: [PATCH bpf-next v3 1/4] bpf/crib: Introduce task

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzYib5jyu90tJYSTEmhpZ-4aF135719V+A7J7pzMj7RpNA@mail.gmail.com>
Date: Wed, 6 Nov 2024 14:10:08 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Juntong Deng <juntong.deng@...look.com>, 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 v3 1/4] bpf/crib: Introduce task_file open-coded
 iterator kfuncs

On Wed, Nov 6, 2024 at 1:32 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Wed, Nov 6, 2024 at 11:39 AM Juntong Deng <juntong.deng@...look.com> wrote:
> >
> > This patch adds the open-coded iterator style process file iterator
> > kfuncs bpf_iter_task_file_{new,next,destroy} that iterates over all
> > files opened by the specified process.
>
> This is ok.
>
> > In addition, this patch adds bpf_iter_task_file_get_fd() getter to get
> > the file descriptor corresponding to the file in the current iteration.
>
> Unnecessary. Use CORE to read iter internal fields.

+1, I suggested to use __ksym approach and compare to f_op

>
> > The reference to struct file acquired by the previous
> > bpf_iter_task_file_next() is released in the next
> > bpf_iter_task_file_next(), and the last reference is released in the
> > last bpf_iter_task_file_next() that returns NULL.
> >
> > In the bpf_iter_task_file_destroy(), if the iterator does not iterate to
> > the end, then the last struct file reference is released at this time.
> >
> > Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> > ---
> >  kernel/bpf/helpers.c   |  4 ++
> >  kernel/bpf/task_iter.c | 96 ++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 100 insertions(+)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index 395221e53832..1f0f7ca1c47a 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -3096,6 +3096,10 @@ BTF_ID_FLAGS(func, bpf_iter_css_destroy, KF_ITER_DESTROY)
> >  BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS | KF_RCU_PROTECTED)
> >  BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
> >  BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
> > +BTF_ID_FLAGS(func, bpf_iter_task_file_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
> > +BTF_ID_FLAGS(func, bpf_iter_task_file_next, KF_ITER_NEXT | KF_RET_NULL)
> > +BTF_ID_FLAGS(func, bpf_iter_task_file_get_fd)
> > +BTF_ID_FLAGS(func, bpf_iter_task_file_destroy, KF_ITER_DESTROY)
> >  BTF_ID_FLAGS(func, bpf_dynptr_adjust)
> >  BTF_ID_FLAGS(func, bpf_dynptr_is_null)
> >  BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> > index 5af9e130e500..32e15403a5a6 100644
> > --- a/kernel/bpf/task_iter.c
> > +++ b/kernel/bpf/task_iter.c
> > @@ -1031,6 +1031,102 @@ __bpf_kfunc void bpf_iter_task_destroy(struct bpf_iter_task *it)
> >  {
> >  }
> >
> > +struct bpf_iter_task_file {
> > +       __u64 __opaque[3];
> > +} __aligned(8);
> > +
> > +struct bpf_iter_task_file_kern {
> > +       struct task_struct *task;
> > +       struct file *file;
> > +       int fd;
> > +} __aligned(8);
> > +
> > +/**
> > + * bpf_iter_task_file_new() - Initialize a new task file iterator for a task,
> > + * used to iterate over all files opened by a specified task
> > + *
> > + * @it: the new bpf_iter_task_file to be created
> > + * @task: a pointer pointing to a task to be iterated over
> > + */
> > +__bpf_kfunc int bpf_iter_task_file_new(struct bpf_iter_task_file *it,
> > +               struct task_struct *task)
> > +{
> > +       struct bpf_iter_task_file_kern *kit = (void *)it;
> > +
> > +       BUILD_BUG_ON(sizeof(struct bpf_iter_task_file_kern) > sizeof(struct bpf_iter_task_file));
> > +       BUILD_BUG_ON(__alignof__(struct bpf_iter_task_file_kern) !=
> > +                    __alignof__(struct bpf_iter_task_file));
> > +
> > +       kit->task = task;
>
> This is broken, since task refcnt can drop while iter is running.

I noticed this as well, but I thought that given KF_TRUSTED_ARGS we
should have a guarantee that the task survives the iteration? Am I
mistaken?

>
> Before doing any of that I'd like to see a long term path for crib.
> All these small additions are ok if they're generic and useful elsewhere.
> I'm afraid there is no path forward for crib itself though.
>
> pw-bot: cr