Re: [PATCH bpf-next 1/2] bpf: Add bpf_get_task_cmdline kfunc

[Tao Chen]

在 2025/11/26 07:32, Andrii Nakryiko 写道:
> On Fri, Nov 21, 2025 at 5:17 PM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> > On Tue, Nov 18, 2025 at 4:58 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> > > Add the bpf_get_task_cmdline kfunc. One use case is as follows: In
> > > production environments, there are often short-lived script tasks executed,
> > > and sometimes these tasks may cause stability issues. It is desirable to
> > > detect these script tasks via eBPF. The common approach is to check
> > > the process name, but it can be difficult to distinguish specific
> > > tasks in some cases. Take the shell as an example: some tasks are
> > > started via bash xxx.sh – their process name is bash, but the script
> > > name of the task can be obtained through the cmdline. Additionally,
> > > myabe this is helpful for security auditing purposes.
> >
> > maybe
> >
> > > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > > ---
> > >   kernel/bpf/helpers.c | 22 ++++++++++++++++++++++
> > >   1 file changed, 22 insertions(+)
> > >
> > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > > index 865b0dae38d..7cac17d58d5 100644
> > > --- a/kernel/bpf/helpers.c
> > > +++ b/kernel/bpf/helpers.c
> > > @@ -2685,6 +2685,27 @@ __bpf_kfunc struct task_struct *bpf_task_from_pid(s32 pid)
> > >          return p;
> > >   }
> > >
> > > +/*
> > > + * bpf_get_task_cmdline - Get the cmdline to a buffer
> > > + *
> > > + * @task: The task whose cmdline to get.
> > > + * @buffer: The buffer to save cmdline info.
> > > + * @len: The length of the buffer.
> > > + *
> > > + * Return: the size of the cmdline field copied. Note that the copy does
> > > + * not guarantee an ending NULL byte. A negative error code on failure.
> > > + */
> > > +__bpf_kfunc int bpf_get_task_cmdline(struct task_struct *task, char *buffer, size_t len)
> >
> > 'size_t len' doesn't make the verifier track the size of the buffer.
> > while 'char *buffer' tells the verifier to check that _one_ byte is available.
> > So this is buggy.
> >
> > In general the kfunc seems useful, but selftest in patch 2 is just bad
>
> Besides that mm->arg_lock spinlock (which I don't think matters all
> that much for BPF programs), is there anything special in
> get_cmdline() that BPF program cannot just implemented? Ultimately,
> it's just copying mm->arg_start and mm->env_start zero-separated
> strings, no? We have bpf_copy_from_user_task_str() and also
> dynptr-based equivalent of it for even more variable-length
> flexibility. That should be all one needs, no?

From a quick look at how both are implemented, it seems that way.
Hold off on this patch for now. I will move forward if we find something 
new.

> > + ret = bpf_get_task_cmdline(task, buf, sizeof(buf));
> > + if (ret < 0)
> > +    err = 1;
> > +
> > + return 0;
> > +}
> >
> > it's not testing much.
> >
> > Also you must explain the true motivation for the kfunc.
> > "maybe helpful for security" is too vague.
> > Do you have a proprietary bpf-lsm that needs it?
> > What is the exact use case?
> >
> > pw-bot: cr


--
Best Regards
Tao Chen