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    Subject[PATCH bpf-next 1/2] bpf: Add bpf_task_from_pid() kfunc
    Date
    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>
    ---
    kernel/bpf/helpers.c | 20 ++++++++++++++++++++
    1 file changed, 20 insertions(+)

    diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
    index 9e8a5557ea8d..d5a849d44a35 100644
    --- a/kernel/bpf/helpers.c
    +++ b/kernel/bpf/helpers.c
    @@ -1879,6 +1879,25 @@ void bpf_task_release(struct task_struct *p)
    put_task_struct_rcu_user(p);
    }

    +/**
    + * 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;
    @@ -1904,6 +1923,7 @@ 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)
    +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 = {
    --
    2.38.1
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