linux-kernel - [PATCH net 1/4] umh: add exit routine for UMH process

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Date:   Mon, 31 Dec 2018 01:31:43 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, daniel@...earbox.net, ast@...nel.org,
        mcgrof@...nel.org
Cc:     ap420073@...il.com
Subject: [PATCH net 1/4] umh: add exit routine for UMH process

A UMH process which is created by the fork_usermode_blob() such as
bpfilter needs to release members of the umh_info when process is
terminated.
But the do_exit() does not release members of the umh_info. hence module
which uses UMH needs own code to detect whether UMH process is
terminated or not.
But this implementation needs extra code for checking the status of
UMH process. it eventually makes the code more complex.

The exit_umh() does not release members of the umh_info.
Hence umh_info->cleanup callback should release both members of the
umh_info and the private data.

Suggested-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Taehee Yoo <ap420073@...il.com>
---
 include/linux/umh.h |  4 ++++
 kernel/exit.c       |  1 +
 kernel/umh.c        | 27 +++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/include/linux/umh.h b/include/linux/umh.h
index 235f51b62c71..c645f0a19103 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -47,6 +47,8 @@ struct umh_info {
 	const char *cmdline;
 	struct file *pipe_to_umh;
 	struct file *pipe_from_umh;
+	struct list_head list;
+	void (*cleanup)(struct umh_info *info);
 	pid_t pid;
 };
 int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
@@ -75,6 +77,8 @@ static inline void usermodehelper_enable(void)
 	__usermodehelper_set_disable_depth(UMH_ENABLED);
 }
 
+void exit_umh(struct task_struct *tsk);
+
 extern int usermodehelper_read_trylock(void);
 extern long usermodehelper_read_lock_wait(long timeout);
 extern void usermodehelper_read_unlock(void);
diff --git a/kernel/exit.c b/kernel/exit.c
index 0e21e6d21f35..63ce4c958390 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -866,6 +866,7 @@ void __noreturn do_exit(long code)
 	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
 	exit_thread(tsk);
+	exit_umh(tsk);
 
 	/*
 	 * Flush inherited counters to the parent - before the parent
diff --git a/kernel/umh.c b/kernel/umh.c
index 0baa672e023c..9b2238e440eb 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -37,6 +37,8 @@ static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
 static DEFINE_SPINLOCK(umh_sysctl_lock);
 static DECLARE_RWSEM(umhelper_sem);
+static LIST_HEAD(umh_list);
+static DEFINE_MUTEX(umh_list_lock);
 
 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
@@ -517,6 +519,11 @@ int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 		goto out;
 
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
+	if (!err) {
+		mutex_lock(&umh_list_lock);
+		list_add(&info->list, &umh_list);
+		mutex_unlock(&umh_list_lock);
+	}
 out:
 	fput(file);
 	return err;
@@ -679,6 +686,26 @@ static int proc_cap_handler(struct ctl_table *table, int write,
 	return 0;
 }
 
+void exit_umh(struct task_struct *tsk)
+{
+	struct umh_info *info;
+	pid_t pid = tsk->pid;
+
+	mutex_lock(&umh_list_lock);
+	list_for_each_entry(info, &umh_list, list) {
+		if (info->pid == pid) {
+			list_del(&info->list);
+			mutex_unlock(&umh_list_lock);
+			goto out;
+		}
+	}
+	mutex_unlock(&umh_list_lock);
+	return;
+out:
+	if (info->cleanup)
+		info->cleanup(info);
+}
+
 struct ctl_table usermodehelper_table[] = {
 	{
 		.procname	= "bset",
-- 
2.17.1