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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: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20221122145300.251210-2-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
David Vernet 2022-11-22 08:52:59 -06:00 committed by Alexei Starovoitov
parent 5bad3587b7
commit 3f0e6f2b41
1 changed files with 20 additions and 1 deletions
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21
kernel/bpf/helpers.c
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@ -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 = {