linux/kernel/bpf/task_iter.c
Yonghong Song 04901aab40 bpf: Fix a task_iter bug caused by a merge conflict resolution
Latest bpf tree has a bug for bpf_iter selftest:

  $ ./test_progs -n 4/25
  test_bpf_sk_storage_get:PASS:bpf_iter_bpf_sk_storage_helpers__open_and_load 0 nsec
  test_bpf_sk_storage_get:PASS:socket 0 nsec
  ...
  do_dummy_read:PASS:read 0 nsec
  test_bpf_sk_storage_get:FAIL:bpf_map_lookup_elem map value wasn't set correctly
                          (expected 1792, got -1, err=0)
  #4/25 bpf_sk_storage_get:FAIL
  #4 bpf_iter:FAIL
  Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED

When doing merge conflict resolution, Commit 4bfc471484 missed to
save curr_task to seq_file private data. The task pointer in seq_file
private data is passed to bpf program. This caused NULL-pointer task
passed to bpf program which will immediately return upon checking
whether task pointer is NULL.

This patch added back the assignment of curr_task to seq_file private
data and fixed the issue.

Fixes: 4bfc471484 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20201231052418.577024-1-yhs@fb.com
2021-01-03 01:41:32 +01:00

345 lines
7.8 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2020 Facebook */
#include <linux/init.h>
#include <linux/namei.h>
#include <linux/pid_namespace.h>
#include <linux/fs.h>
#include <linux/fdtable.h>
#include <linux/filter.h>
#include <linux/btf_ids.h>
struct bpf_iter_seq_task_common {
struct pid_namespace *ns;
};
struct bpf_iter_seq_task_info {
/* The first field must be struct bpf_iter_seq_task_common.
* this is assumed by {init, fini}_seq_pidns() callback functions.
*/
struct bpf_iter_seq_task_common common;
u32 tid;
};
static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
u32 *tid,
bool skip_if_dup_files)
{
struct task_struct *task = NULL;
struct pid *pid;
rcu_read_lock();
retry:
pid = find_ge_pid(*tid, ns);
if (pid) {
*tid = pid_nr_ns(pid, ns);
task = get_pid_task(pid, PIDTYPE_PID);
if (!task) {
++*tid;
goto retry;
} else if (skip_if_dup_files && !thread_group_leader(task) &&
task->files == task->group_leader->files) {
put_task_struct(task);
task = NULL;
++*tid;
goto retry;
}
}
rcu_read_unlock();
return task;
}
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);
if (!task)
return NULL;
if (*pos == 0)
++*pos;
return task;
}
static void *task_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct bpf_iter_seq_task_info *info = seq->private;
struct task_struct *task;
++*pos;
++info->tid;
put_task_struct((struct task_struct *)v);
task = task_seq_get_next(info->common.ns, &info->tid, false);
if (!task)
return NULL;
return task;
}
struct bpf_iter__task {
__bpf_md_ptr(struct bpf_iter_meta *, meta);
__bpf_md_ptr(struct task_struct *, task);
};
DEFINE_BPF_ITER_FUNC(task, struct bpf_iter_meta *meta, struct task_struct *task)
static int __task_seq_show(struct seq_file *seq, struct task_struct *task,
bool in_stop)
{
struct bpf_iter_meta meta;
struct bpf_iter__task ctx;
struct bpf_prog *prog;
meta.seq = seq;
prog = bpf_iter_get_info(&meta, in_stop);
if (!prog)
return 0;
meta.seq = seq;
ctx.meta = &meta;
ctx.task = task;
return bpf_iter_run_prog(prog, &ctx);
}
static int task_seq_show(struct seq_file *seq, void *v)
{
return __task_seq_show(seq, v, false);
}
static void task_seq_stop(struct seq_file *seq, void *v)
{
if (!v)
(void)__task_seq_show(seq, v, true);
else
put_task_struct((struct task_struct *)v);
}
static const struct seq_operations task_seq_ops = {
.start = task_seq_start,
.next = task_seq_next,
.stop = task_seq_stop,
.show = task_seq_show,
};
struct bpf_iter_seq_task_file_info {
/* The first field must be struct bpf_iter_seq_task_common.
* this is assumed by {init, fini}_seq_pidns() callback functions.
*/
struct bpf_iter_seq_task_common common;
struct task_struct *task;
u32 tid;
u32 fd;
};
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;
struct task_struct *curr_task;
unsigned int curr_fd = info->fd;
/* If this function returns a non-NULL file object,
* it held a reference to the task/file.
* Otherwise, it does not hold any reference.
*/
again:
if (info->task) {
curr_task = info->task;
curr_fd = info->fd;
} else {
curr_task = task_seq_get_next(ns, &curr_tid, true);
if (!curr_task) {
info->task = NULL;
info->tid = curr_tid;
return NULL;
}
/* set info->task and info->tid */
info->task = curr_task;
if (curr_tid == info->tid) {
curr_fd = info->fd;
} else {
info->tid = curr_tid;
curr_fd = 0;
}
}
rcu_read_lock();
for (;; curr_fd++) {
struct file *f;
f = task_lookup_next_fd_rcu(curr_task, &curr_fd);
if (!f)
break;
if (!get_file_rcu(f))
continue;
/* set info->fd */
info->fd = curr_fd;
rcu_read_unlock();
return f;
}
/* the current task is done, go to the next task */
rcu_read_unlock();
put_task_struct(curr_task);
info->task = NULL;
info->fd = 0;
curr_tid = ++(info->tid);
goto again;
}
static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
{
struct bpf_iter_seq_task_file_info *info = seq->private;
struct file *file;
info->task = NULL;
file = task_file_seq_get_next(info);
if (file && *pos == 0)
++*pos;
return file;
}
static void *task_file_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct bpf_iter_seq_task_file_info *info = seq->private;
++*pos;
++info->fd;
fput((struct file *)v);
return task_file_seq_get_next(info);
}
struct bpf_iter__task_file {
__bpf_md_ptr(struct bpf_iter_meta *, meta);
__bpf_md_ptr(struct task_struct *, task);
u32 fd __aligned(8);
__bpf_md_ptr(struct file *, file);
};
DEFINE_BPF_ITER_FUNC(task_file, struct bpf_iter_meta *meta,
struct task_struct *task, u32 fd,
struct file *file)
static int __task_file_seq_show(struct seq_file *seq, struct file *file,
bool in_stop)
{
struct bpf_iter_seq_task_file_info *info = seq->private;
struct bpf_iter__task_file ctx;
struct bpf_iter_meta meta;
struct bpf_prog *prog;
meta.seq = seq;
prog = bpf_iter_get_info(&meta, in_stop);
if (!prog)
return 0;
ctx.meta = &meta;
ctx.task = info->task;
ctx.fd = info->fd;
ctx.file = file;
return bpf_iter_run_prog(prog, &ctx);
}
static int task_file_seq_show(struct seq_file *seq, void *v)
{
return __task_file_seq_show(seq, v, false);
}
static void task_file_seq_stop(struct seq_file *seq, void *v)
{
struct bpf_iter_seq_task_file_info *info = seq->private;
if (!v) {
(void)__task_file_seq_show(seq, v, true);
} else {
fput((struct file *)v);
put_task_struct(info->task);
info->task = NULL;
}
}
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));
return 0;
}
static void fini_seq_pidns(void *priv_data)
{
struct bpf_iter_seq_task_common *common = priv_data;
put_pid_ns(common->ns);
}
static const struct seq_operations task_file_seq_ops = {
.start = task_file_seq_start,
.next = task_file_seq_next,
.stop = task_file_seq_stop,
.show = task_file_seq_show,
};
BTF_ID_LIST(btf_task_file_ids)
BTF_ID(struct, task_struct)
BTF_ID(struct, file)
static const struct bpf_iter_seq_info task_seq_info = {
.seq_ops = &task_seq_ops,
.init_seq_private = init_seq_pidns,
.fini_seq_private = fini_seq_pidns,
.seq_priv_size = sizeof(struct bpf_iter_seq_task_info),
};
static struct bpf_iter_reg task_reg_info = {
.target = "task",
.feature = BPF_ITER_RESCHED,
.ctx_arg_info_size = 1,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__task, task),
PTR_TO_BTF_ID_OR_NULL },
},
.seq_info = &task_seq_info,
};
static const struct bpf_iter_seq_info task_file_seq_info = {
.seq_ops = &task_file_seq_ops,
.init_seq_private = init_seq_pidns,
.fini_seq_private = fini_seq_pidns,
.seq_priv_size = sizeof(struct bpf_iter_seq_task_file_info),
};
static struct bpf_iter_reg task_file_reg_info = {
.target = "task_file",
.feature = BPF_ITER_RESCHED,
.ctx_arg_info_size = 2,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__task_file, task),
PTR_TO_BTF_ID_OR_NULL },
{ offsetof(struct bpf_iter__task_file, file),
PTR_TO_BTF_ID_OR_NULL },
},
.seq_info = &task_file_seq_info,
};
static int __init task_iter_init(void)
{
int ret;
task_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
ret = bpf_iter_reg_target(&task_reg_info);
if (ret)
return ret;
task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
return bpf_iter_reg_target(&task_file_reg_info);
}
late_initcall(task_iter_init);