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Message-ID: <123407cd-f439-7158-1c06-7cd6f10ba8e9@iogearbox.net>
Date: Mon, 25 Mar 2019 15:17:03 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Javier Honduvilla Coto <javierhonduco@...com>,
netdev@...r.kernel.org
Cc: yhs@...com, kernel-team@...com
Subject: Re: [PATCH v4 bpf-next 1/3] bpf: add bpf_progenyof helper
On 03/22/2019 11:38 PM, Javier Honduvilla Coto wrote:
> This patch adds the bpf_progenyof helper which receives a PID and returns
> 1 if the process currently being executed is in the process hierarchy
> including itself or 0 if not.
>
> This is very useful in tracing programs when we want to filter by a
> given PID and all the children it might spawn. The current workarounds
> most people implement for this purpose have issues:
>
> - Attaching to process spawning syscalls and dynamically add those PIDs
> to some bpf map that would be used to filter is cumbersome and
> potentially racy.
> - Unrolling some loop to perform what this helper is doing consumes lots
> of instructions. That and the impossibility to jump backwards makes it
> really hard to be correct in really large process chains.
>
> Signed-off-by: Javier Honduvilla Coto <javierhonduco@...com>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 10 +++++++++-
> kernel/bpf/core.c | 1 +
> kernel/bpf/helpers.c | 32 ++++++++++++++++++++++++++++++++
> kernel/trace/bpf_trace.c | 2 ++
> 5 files changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f62897198844..bd0d2b38e7d5 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -930,6 +930,7 @@ extern const struct bpf_func_proto bpf_sk_redirect_map_proto;
> extern const struct bpf_func_proto bpf_spin_lock_proto;
> extern const struct bpf_func_proto bpf_spin_unlock_proto;
> extern const struct bpf_func_proto bpf_get_local_storage_proto;
> +extern const struct bpf_func_proto bpf_progenyof_proto;
>
> /* Shared helpers among cBPF and eBPF. */
> void bpf_user_rnd_init_once(void);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 3c04410137d9..cf54cc739bf4 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2463,6 +2463,13 @@ union bpf_attr {
> * Return
> * 0 if iph and th are a valid SYN cookie ACK, or a negative error
> * otherwise.
> + * int bpf_progenyof(int pid)
> + * Description
> + * This helper is useful in programs that want to filter events
> + * happening to a pid of any of its descendants.
> + * Return
> + * 1 if the currently executing process' pid is in the process
> + * hierarchy of the passed pid. 0 Otherwise.
What about the -EINVAL?
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -2565,7 +2572,8 @@ union bpf_attr {
> FN(skb_ecn_set_ce), \
> FN(get_listener_sock), \
> FN(skc_lookup_tcp), \
> - FN(tcp_check_syncookie),
> + FN(tcp_check_syncookie), \
> + FN(progenyof),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ff09d32a8a1b..437986497468 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2044,6 +2044,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
> const struct bpf_func_proto bpf_get_current_comm_proto __weak;
> const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
> const struct bpf_func_proto bpf_get_local_storage_proto __weak;
> +const struct bpf_func_proto bpf_progenyof_proto __weak;
>
> const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
> {
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index a411fc17d265..f093b35d1ba8 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -18,6 +18,7 @@
> #include <linux/sched.h>
> #include <linux/uidgid.h>
> #include <linux/filter.h>
> +#include <linux/init_task.h>
>
> /* If kernel subsystem is allowing eBPF programs to call this function,
> * inside its own verifier_ops->get_func_proto() callback it should return
> @@ -364,3 +365,34 @@ const struct bpf_func_proto bpf_get_local_storage_proto = {
> };
> #endif
> #endif
> +
> +BPF_CALL_1(bpf_progenyof, int, pid)
Nit: could we add a more descriptive helper name? What's progenyof? Also s/int/pid_t/?
> +{
> + int result = 0;
> + struct task_struct *task = current;
> +
> + WARN_ON(!rcu_read_lock_held());
This is not needed since it's guaranteed in BPF.
> + if (unlikely(!task))
> + return -EINVAL;
> +
> + if (pid == 0)
> + return 1;
> +
> + while (task != &init_task) {
> + if (task->pid == pid) {
> + result = 1;
> + break;
> + }
> + task = rcu_dereference(task->real_parent);
> + }
> +
> + return result;
> +}
> +
> +const struct bpf_func_proto bpf_progenyof_proto = {
> + .func = bpf_progenyof,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_ANYTHING,
> +};
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d64c00afceb5..e69283d423ff 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -599,6 +599,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_get_prandom_u32_proto;
> case BPF_FUNC_probe_read_str:
> return &bpf_probe_read_str_proto;
> + case BPF_FUNC_progenyof:
> + return &bpf_progenyof_proto;
> #ifdef CONFIG_CGROUPS
> case BPF_FUNC_get_current_cgroup_id:
> return &bpf_get_current_cgroup_id_proto;
>
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