Commit 3f0e6f2b authored by David Vernet's avatar David Vernet Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_task_from_pid() kfunc 



Callers can currently store tasks as kptrs using bpf_task_acquire(),
bpf_task_kptr_get(), and bpf_task_release(). These are useful if a
caller already has a struct task_struct *, but there may be some callers
who only have a pid, and want to look up the associated struct
task_struct * from that to e.g. find task->comm.

This patch therefore adds a new bpf_task_from_pid() kfunc which allows
BPF programs to get a struct task_struct * kptr from a pid.

Signed-off-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20221122145300.251210-2-void@manifault.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 5bad3587

kernel/bpf/helpers.c

+20 −1
Original line number Diff line number Diff line
@@ -1959,6 +1959,25 @@ struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) 
}

#endif /* CONFIG_CGROUPS */



/**

 * bpf_task_from_pid - Find a struct task_struct from its pid by looking it up

 * in the root pid namespace idr. If a task is returned, it must either be

 * stored in a map, or released with bpf_task_release().

 * @pid: The pid of the task being looked up.

 */

struct task_struct *bpf_task_from_pid(s32 pid)

{

	struct task_struct *p;



	rcu_read_lock();

	p = find_task_by_pid_ns(pid, &init_pid_ns);

	if (p)

		bpf_task_acquire(p);

	rcu_read_unlock();



	return p;

}



void *bpf_cast_to_kern_ctx(void *obj)

{

	return obj;
@@ -1984,13 +2003,13 @@ BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL) 
BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)

BTF_ID_FLAGS(func, bpf_task_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)



#ifdef CONFIG_CGROUPS

BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)

BTF_ID_FLAGS(func, bpf_cgroup_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)

BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)

#endif

BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)

BTF_SET8_END(generic_btf_ids)



static const struct btf_kfunc_id_set generic_kfunc_set = {