Re: [PATCH bpf-next 1/2] bpf: implement bpf_send_signal_pid/tgid() helpers

Alexei Starovoitov
2024-07-24T23:23:14Z

On Wed, Jul 24, 2024 at 4:40 AM Puranjay Mohan <puranjay@kernel.org> wrote:
>
> Implement bpf_send_signal_pid and bpf_send_signal_tgid helpers which are
> similar to bpf_send_signal_thread and bpf_send_signal helpers
> respectively but can be used to send signals to other threads and
> processes.

Thanks for working on this!
But it needs more homework.

> #define ___BPF_FUNC_MAPPER(FN, ctx...) \
> FN(unspec, 0, ##ctx) \
> @@ -6006,6 +6041,8 @@ union bpf_attr {
> FN(user_ringbuf_drain, 209, ##ctx) \
> FN(cgrp_storage_get, 210, ##ctx) \
> FN(cgrp_storage_delete, 211, ##ctx) \
> + FN(send_signal_pid, 212, ##ctx) \
> + FN(send_signal_tgid, 213, ##ctx) \

We stopped adding helpers long ago.
They need to be kfuncs.

> /* */
>
> /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index cd098846e251..f1e58122600d 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -839,21 +839,30 @@ static void do_bpf_send_signal(struct irq_work *entry)
> put_task_struct(work->task);
> }
>
> -static int bpf_send_signal_common(u32 sig, enum pid_type type)
> +static int bpf_send_signal_common(u32 sig, enum pid_type type, u32 pid)
> {
> struct send_signal_irq_work *work = NULL;
> + struct task_struct *tsk;
> +
> + if (pid) {
> + tsk = find_task_by_vpid(pid);

by vpid ?

tracing bpf prog will have "random" current and "random" pidns.

Should it be find_get_task vs find_task too ?

Should kfunc take 'task' parameter instead
received from bpf_task_from_pid() ?

two kfuncs for pid/tgid is overkill. Combine into one?

> + if (!tsk)
> + return -ESRCH;
> + } else {
> + tsk = current;
> + }

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