On 04/10/2019 10:36 PM, Javier Honduvilla Coto wrote:
> This patch adds the bpf_descendant_of helper which accepts a PID and
> returns 1 if the PID of the process currently being executed is a
> descendant of it or if it's itself. Returns 0 otherwise.
>
> 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 <javierhond...@fb.com>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 10 +++++++++-
> kernel/bpf/core.c | 1 +
> kernel/bpf/helpers.c | 27 +++++++++++++++++++++++++++
> kernel/trace/bpf_trace.c | 2 ++
> 5 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 65f7094c40b4..0539999f07f3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -967,6 +967,7 @@ 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_descendant_of_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 af1cbd951f26..f707b286c21d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2493,6 +2493,13 @@ union bpf_attr {
> * Return
> * 0 if iph and th are a valid SYN cookie ACK, or a negative error
> * otherwise.
> + * int bpf_descendant_of(pid_t pid)
Small nit: Looks good to go, but please add a newline before the new helper
description like all the rest in there.
> + * Description
> + * This helper is useful in programs that want to filter events
> + * happening to a pid or to any of its descendants.
One more thing that would be helpful is to add a short description here that
this helper can be used in combination with bpf_get_current_pid_tgid(), and
that pid here is representation from init pid namespace if I grok it correctly.
> + * Return
> + * 1 if the passed pid is an ancestor of the currently executing
> + * process' pid or equal to it.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -2595,7 +2602,8 @@ 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(descendant_of),
>
> /* 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 ace8c22c8b0e..df93d7157657 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2046,6 +2046,7 @@ 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_descendant_of_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..d04186c69042 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 +365,29 @@ const struct bpf_func_proto bpf_get_local_storage_proto
> = {
> };
> #endif
> #endif
> +
> +BPF_CALL_1(bpf_descendant_of, pid_t, pid)
> +{
> + int result = 0;
> + struct task_struct *task = current;
> +
> + 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_descendant_of_proto = {
> + .func = bpf_descendant_of,
> + .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..0968e38a2aae 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_descendant_of:
> + return &bpf_descendant_of_proto;
> #ifdef CONFIG_CGROUPS
> case BPF_FUNC_get_current_cgroup_id:
> return &bpf_get_current_cgroup_id_proto;
>
