bpf: Add task and task/file iterator targets

Only the tasks belonging to "current" pid namespace
are enumerated.

For task/file target, the bpf program will have access to
  struct task_struct *task
  u32 fd
  struct file *file
where fd/file is an open file for the task.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200509175911.2476407-1-yhs@fb.com

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index b2b5eefc5254f5cf6967e09ac35aa73d0ae23d55..37b2d86201533168578ae300d346a61b0bc67c20 100644 (file)
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -2,7 +2,7 @@
 obj-y := core.o
 CFLAGS_core.o += $(call cc-disable-warning, override-init)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
new file mode 100644 (file)
index 0000000..aeed662
--- /dev/null
+++ b/kernel/bpf/task_iter.c
@@ -0,0 +1,333 @@
+// 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>
+
+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)
+{
+       struct task_struct *task = NULL;
+       struct pid *pid;
+
+       rcu_read_lock();
+       pid = idr_get_next(&ns->idr, tid);
+       if (pid)
+               task = get_pid_task(pid, PIDTYPE_PID);
+       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);
+       if (!task)
+               return NULL;
+
+       ++*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);
+       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;
+       struct files_struct *files;
+       u32 tid;
+       u32 fd;
+};
+
+static struct file *
+task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info,
+                      struct task_struct **task, struct files_struct **fstruct)
+{
+       struct pid_namespace *ns = info->common.ns;
+       u32 curr_tid = info->tid, max_fds;
+       struct files_struct *curr_files;
+       struct task_struct *curr_task;
+       int curr_fd = info->fd;
+
+       /* If this function returns a non-NULL file object,
+        * it held a reference to the task/files_struct/file.
+        * Otherwise, it does not hold any reference.
+        */
+again:
+       if (*task) {
+               curr_task = *task;
+               curr_files = *fstruct;
+               curr_fd = info->fd;
+       } else {
+               curr_task = task_seq_get_next(ns, &curr_tid);
+               if (!curr_task)
+                       return NULL;
+
+               curr_files = get_files_struct(curr_task);
+               if (!curr_files) {
+                       put_task_struct(curr_task);
+                       curr_tid = ++(info->tid);
+                       info->fd = 0;
+                       goto again;
+               }
+
+               /* set *fstruct, *task and info->tid */
+               *fstruct = curr_files;
+               *task = curr_task;
+               if (curr_tid == info->tid) {
+                       curr_fd = info->fd;
+               } else {
+                       info->tid = curr_tid;
+                       curr_fd = 0;
+               }
+       }
+
+       rcu_read_lock();
+       max_fds = files_fdtable(curr_files)->max_fds;
+       for (; curr_fd < max_fds; curr_fd++) {
+               struct file *f;
+
+               f = fcheck_files(curr_files, curr_fd);
+               if (!f)
+                       continue;
+
+               /* set info->fd */
+               info->fd = curr_fd;
+               get_file(f);
+               rcu_read_unlock();
+               return f;
+       }
+
+       /* the current task is done, go to the next task */
+       rcu_read_unlock();
+       put_files_struct(curr_files);
+       put_task_struct(curr_task);
+       *task = NULL;
+       *fstruct = 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 files_struct *files = NULL;
+       struct task_struct *task = NULL;
+       struct file *file;
+
+       file = task_file_seq_get_next(info, &task, &files);
+       if (!file) {
+               info->files = NULL;
+               info->task = NULL;
+               return NULL;
+       }
+
+       ++*pos;
+       info->task = task;
+       info->files = files;
+
+       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;
+       struct files_struct *files = info->files;
+       struct task_struct *task = info->task;
+       struct file *file;
+
+       ++*pos;
+       ++info->fd;
+       fput((struct file *)v);
+       file = task_file_seq_get_next(info, &task, &files);
+       if (!file) {
+               info->files = NULL;
+               info->task = NULL;
+               return NULL;
+       }
+
+       info->task = task;
+       info->files = files;
+
+       return file;
+}
+
+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_files_struct(info->files);
+               put_task_struct(info->task);
+               info->files = NULL;
+               info->task = NULL;
+       }
+}
+
+static int init_seq_pidns(void *priv_data)
+{
+       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,
+};
+
+static int __init task_iter_init(void)
+{
+       struct bpf_iter_reg task_file_reg_info = {
+               .target                 = "task_file",
+               .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),
+       };
+       struct bpf_iter_reg task_reg_info = {
+               .target                 = "task",
+               .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),
+       };
+       int ret;
+
+       ret = bpf_iter_reg_target(&task_reg_info);
+       if (ret)
+               return ret;
+
+       return bpf_iter_reg_target(&task_file_reg_info);
+}
+late_initcall(task_iter_init);