[PATCH bpf-next v9 1/5] bpf: Parameterize task iterators.

Kui-Feng Lee
2022-08-31T02:38:23Z

Allow creating an iterator that loops through resources of one
thread/process.

People could only create iterators to loop through all resources of
files, vma, and tasks in the system, even though they were interested
in only the resources of a specific task or process. Passing the
additional parameters, people can now create an iterator to go
through all resources or only the resources of a task.

Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 25 +++++
include/uapi/linux/bpf.h | 6 ++
kernel/bpf/task_iter.c | 191 +++++++++++++++++++++++++++++----
tools/include/uapi/linux/bpf.h | 6 ++
4 files changed, 206 insertions(+), 22 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9c1674973e03..31ac2c1181f5 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1730,6 +1730,27 @@ int bpf_obj_get_user(const char __user *pathname, int flags);
extern int bpf_iter_ ## target(args); \
int __init bpf_iter_ ## target(args) { return 0; }

+/*
+ * The task type of iterators.
+ *
+ * For BPF task iterators, they can be parameterized with various
+ * parameters to visit only some of tasks.
+ *
+ * BPF_TASK_ITER_ALL (default)
+ * Iterate over resources of every task.
+ *
+ * BPF_TASK_ITER_TID
+ * Iterate over resources of a task/tid.
+ *
+ * BPF_TASK_ITER_TGID
+ * Iterate over resources of every task of a process / task group.
+ */
+enum bpf_iter_task_type {
+ BPF_TASK_ITER_ALL = 0,
+ BPF_TASK_ITER_TID,
+ BPF_TASK_ITER_TGID,
+};
+
struct bpf_iter_aux_info {
/* for map_elem iter */
struct bpf_map *map;
@@ -1739,6 +1760,10 @@ struct bpf_iter_aux_info {
struct cgroup *start; /* starting cgroup */
enum bpf_cgroup_iter_order order;
} cgroup;
+ struct {
+ enum bpf_iter_task_type type;
+ u32 pid;
+ } task;
};

typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 962960a98835..f212a19eda06 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -110,6 +110,12 @@ union bpf_iter_link_info {
__u32 cgroup_fd;
__u64 cgroup_id;
} cgroup;
+ /* Parameters of task iterators. */
+ struct {
+ __u32 tid;
+ __u32 pid;
+ __u32 pid_fd;
+ } task;
};

/* BPF syscall commands, see bpf(2) man-page for more details. */
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 8c921799def4..93779a021697 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -12,6 +12,9 @@

struct bpf_iter_seq_task_common {
struct pid_namespace *ns;
+ enum bpf_iter_task_type type;
+ u32 pid;
+ u32 pid_visiting;
};

struct bpf_iter_seq_task_info {
@@ -22,18 +25,114 @@ struct bpf_iter_seq_task_info {
u32 tid;
};

-static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
+static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_common *common,
+ u32 *tid,
+ bool skip_if_dup_files)
+{
+ struct task_struct *task, *next_task;
+ struct pid *pid;
+ u32 saved_tid;
+
+ if (!*tid) {
+ /* The first time, the iterator calls this function. */
+ pid = find_pid_ns(common->pid, common->ns);
+ if (!pid)
+ return NULL;
+
+ task = get_pid_task(pid, PIDTYPE_TGID);
+ if (!task)
+ return NULL;
+
+ *tid = common->pid;
+ common->pid_visiting = common->pid;
+
+ return task;
+ }
+
+ /* The value of *tid hasn't changed since the last time the
+ * iterator called this function.
+ *
+ * A caller will increase *tid by 1 to move to the next task.
+ * In other words, we should return the task of the given
+ * value of *tid if it hasn't changed since the last time
+ * the iterator called this function.
+ */
+ if (*tid == common->pid_visiting) {
+ pid = find_pid_ns(common->pid_visiting, common->ns);
+ task = get_pid_task(pid, PIDTYPE_PID);
+
+ return task;
+ }
+
+ pid = find_pid_ns(common->pid_visiting, common->ns);
+ if (!pid)
+ return NULL;
+
+ task = get_pid_task(pid, PIDTYPE_PID);
+ if (!task)
+ return NULL;
+
+retry:
+ next_task = next_thread(task);
+ put_task_struct(task);
+ if (!next_task)
+ return NULL;
+
+ saved_tid = *tid;
+ *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
+ if (*tid == common->pid) {
+ /* Run out of tasks of a process. The tasks of a
+ * thread_group are linked as circular linked list.
+ */
+ *tid = saved_tid;
+ return NULL;
+ }
+
+ get_task_struct(next_task);
+ common->pid_visiting = *tid;
+
+ if (skip_if_dup_files && task->files == task->group_leader->files) {
+ task = next_task;
+ goto retry;
+ }
+
+ return next_task;
+}
+
+static struct task_struct *task_seq_get_next(struct bpf_iter_seq_task_common *common,
u32 *tid,
bool skip_if_dup_files)
{
struct task_struct *task = NULL;
struct pid *pid;

+ if (common->type == BPF_TASK_ITER_TID) {
+ if (*tid && *tid != common->pid)
+ return NULL;
+ rcu_read_lock();
+ pid = find_pid_ns(common->pid, common->ns);
+ if (pid) {
+ task = get_pid_task(pid, PIDTYPE_TGID);
+ *tid = common->pid;
+ }
+ rcu_read_unlock();
+
+ return task;
+ }
+
+ if (common->type == BPF_TASK_ITER_TGID) {
+ rcu_read_lock();
+ task = task_group_seq_get_next(common, tid, skip_if_dup_files);
+ rcu_read_unlock();
+
+ return task;
+ }
+
rcu_read_lock();
retry:
- pid = find_ge_pid(*tid, ns);
+ pid = find_ge_pid(*tid, common->ns);
if (pid) {
- *tid = pid_nr_ns(pid, ns);
+ *tid = pid_nr_ns(pid, common->ns);
task = get_pid_task(pid, PIDTYPE_PID);
if (!task) {
++*tid;
@@ -56,7 +155,7 @@ static void *task_seq_start(struct seq_file *seq, loff_t *pos)
struct bpf_iter_seq_task_info *info = seq->private;
struct task_struct *task;

- task = task_seq_get_next(info->common.ns, &info->tid, false);
+ task = task_seq_get_next(&info->common, &info->tid, false);
if (!task)
return NULL;

@@ -73,7 +172,7 @@ static void *task_seq_next(struct seq_file *seq, void *v, loff_t *pos)
++*pos;
++info->tid;
put_task_struct((struct task_struct *)v);
- task = task_seq_get_next(info->common.ns, &info->tid, false);
+ task = task_seq_get_next(&info->common, &info->tid, false);
if (!task)
return NULL;

@@ -117,6 +216,45 @@ static void task_seq_stop(struct seq_file *seq, void *v)
put_task_struct((struct task_struct *)v);
}

+static int bpf_iter_attach_task(struct bpf_prog *prog,
+ union bpf_iter_link_info *linfo,
+ struct bpf_iter_aux_info *aux)
+{
+ unsigned int flags;
+ struct pid_namespace *ns;
+ struct pid *pid;
+ pid_t tgid;
+
+ if ((!!linfo->task.tid + !!linfo->task.pid + !!linfo->task.pid_fd) > 1)
+ return -EINVAL;
+
+ aux->task.type = BPF_TASK_ITER_ALL;
+ if (linfo->task.tid != 0) {
+ aux->task.type = BPF_TASK_ITER_TID;
+ aux->task.pid = linfo->task.tid;
+ }
+ if (linfo->task.pid != 0) {
+ aux->task.type = BPF_TASK_ITER_TGID;
+ aux->task.pid = linfo->task.pid;
+ }
+ if (linfo->task.pid_fd != 0) {
+ aux->task.type = BPF_TASK_ITER_TGID;
+ ns = task_active_pid_ns(current);
+ if (IS_ERR(ns))
+ return PTR_ERR(ns);
+
+ pid = pidfd_get_pid(linfo->task.pid_fd, &flags);
+ if (IS_ERR(pid))
+ return PTR_ERR(pid);
+
+ tgid = pid_nr_ns(pid, ns);
+ aux->task.pid = tgid;
+ put_pid(pid);
+ }
+
+ return 0;
+}
+
static const struct seq_operations task_seq_ops = {
.start = task_seq_start,
.next = task_seq_next,
@@ -137,8 +275,7 @@ struct bpf_iter_seq_task_file_info {
static struct file *
task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
{
- struct pid_namespace *ns = info->common.ns;
- u32 curr_tid = info->tid;
+ u32 saved_tid = info->tid;
struct task_struct *curr_task;
unsigned int curr_fd = info->fd;

@@ -151,21 +288,18 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
curr_task = info->task;
curr_fd = info->fd;
} else {
- curr_task = task_seq_get_next(ns, &curr_tid, true);
+ curr_task = task_seq_get_next(&info->common, &info->tid, true);
if (!curr_task) {
info->task = NULL;
- info->tid = curr_tid;
return NULL;
}

- /* set info->task and info->tid */
+ /* set info->task */
info->task = curr_task;
- if (curr_tid == info->tid) {
+ if (saved_tid == info->tid)
curr_fd = info->fd;
- } else {
- info->tid = curr_tid;
+ else
curr_fd = 0;
- }
}

rcu_read_lock();
@@ -186,9 +320,15 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
/* the current task is done, go to the next task */
rcu_read_unlock();
put_task_struct(curr_task);
+
+ if (info->common.type == BPF_TASK_ITER_TID) {
+ info->task = NULL;
+ return NULL;
+ }
+
info->task = NULL;
info->fd = 0;
- curr_tid = ++(info->tid);
+ saved_tid = ++(info->tid);
goto again;
}

@@ -269,6 +409,9 @@ static int init_seq_pidns(void *priv_data, struct bpf_iter_aux_info *aux)
struct bpf_iter_seq_task_common *common = priv_data;

common->ns = get_pid_ns(task_active_pid_ns(current));
+ common->type = aux->task.type;
+ common->pid = aux->task.pid;
+
return 0;
}

@@ -307,11 +450,10 @@ enum bpf_task_vma_iter_find_op {
static struct vm_area_struct *
task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
{
- struct pid_namespace *ns = info->common.ns;
enum bpf_task_vma_iter_find_op op;
struct vm_area_struct *curr_vma;
struct task_struct *curr_task;
- u32 curr_tid = info->tid;
+ u32 saved_tid = info->tid;

/* If this function returns a non-NULL vma, it holds a reference to
* the task_struct, and holds read lock on vma->mm->mmap_lock.
@@ -371,14 +513,13 @@ task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
}
} else {
again:
- curr_task = task_seq_get_next(ns, &curr_tid, true);
+ curr_task = task_seq_get_next(&info->common, &info->tid, true);
if (!curr_task) {
- info->tid = curr_tid + 1;
+ info->tid++;
goto finish;
}

- if (curr_tid != info->tid) {
- info->tid = curr_tid;
+ if (saved_tid != info->tid) {
/* new task, process the first vma */
op = task_vma_iter_first_vma;
} else {
@@ -430,9 +571,12 @@ task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
return curr_vma;

next_task:
+ if (info->common.type == BPF_TASK_ITER_TID)
+ goto finish;
+
put_task_struct(curr_task);
info->task = NULL;
- curr_tid++;
+ info->tid++;
goto again;

finish:
@@ -533,6 +677,7 @@ static const struct bpf_iter_seq_info task_seq_info = {

static struct bpf_iter_reg task_reg_info = {
.target = "task",
+ .attach_target = bpf_iter_attach_task,
.feature = BPF_ITER_RESCHED,
.ctx_arg_info_size = 1,
.ctx_arg_info = {
@@ -551,6 +696,7 @@ static const struct bpf_iter_seq_info task_file_seq_info = {

static struct bpf_iter_reg task_file_reg_info = {
.target = "task_file",
+ .attach_target = bpf_iter_attach_task,
.feature = BPF_ITER_RESCHED,
.ctx_arg_info_size = 2,
.ctx_arg_info = {
@@ -571,6 +717,7 @@ static const struct bpf_iter_seq_info task_vma_seq_info = {

static struct bpf_iter_reg task_vma_reg_info = {
.target = "task_vma",
+ .attach_target = bpf_iter_attach_task,
.feature = BPF_ITER_RESCHED,
.ctx_arg_info_size = 2,
.ctx_arg_info = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index f4ba82a1eace..40935278eede 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -110,6 +110,12 @@ union bpf_iter_link_info {
__u32 cgroup_fd;
__u64 cgroup_id;
} cgroup;
+ /* Parameters of task iterators. */
+ struct {
+ __u32 tid;
+ __u32 pid;
+ __u32 pid_fd;
+ } task;
};

/* BPF syscall commands, see bpf(2) man-page for more details. */
--
2.30.2