Commit e788e066 authored by Paul Menage's avatar Paul Menage Committed by Linus Torvalds
Browse files

cgroup files: move the release_agent file to use typed handlers 



Adds cgroup_release_agent_write() and cgroup_release_agent_show()
methods to handle writing/reading the path to a cgroup hierarchy's
release agent. As a result, cgroup_common_file_read() is now unnecessary.

As part of the change, a previously-tolerated race in
cgroup_release_agent() is avoided by copying the current
release_agent_path prior to calling call_usermode_helper().

Signed-off-by: default avatarPaul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent db3b1497

include/linux/cgroup.h

+2 −0
Original line number Diff line number Diff line
@@ -295,6 +295,8 @@ int cgroup_add_files(struct cgroup *cgrp, 


int cgroup_is_removed(const struct cgroup *cgrp);



int cgroup_lock_live_group(struct cgroup *cgrp);



int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);



int cgroup_task_count(const struct cgroup *cgrp);

kernel/cgroup.c

+57 −68
Original line number Diff line number Diff line
@@ -89,11 +89,7 @@ struct cgroupfs_root { 
	/* Hierarchy-specific flags */

	unsigned long flags;



	/* The path to use for release notifications. No locking

	 * between setting and use - so if userspace updates this

	 * while child cgroups exist, you could miss a

	 * notification. We ensure that it's always a valid

	 * NUL-terminated string */

	/* The path to use for release notifications. */

	char release_agent_path[PATH_MAX];

};
@@ -1329,6 +1325,45 @@ enum cgroup_filetype { 
	FILE_RELEASE_AGENT,

};



/**

 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.

 * @cgrp: the cgroup to be checked for liveness

 *

 * Returns true (with lock held) on success, or false (with no lock

 * held) on failure.

 */

int cgroup_lock_live_group(struct cgroup *cgrp)

{

	mutex_lock(&cgroup_mutex);

	if (cgroup_is_removed(cgrp)) {

		mutex_unlock(&cgroup_mutex);

		return false;

	}

	return true;

}



static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,

				      const char *buffer)

{

	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);

	if (!cgroup_lock_live_group(cgrp))

		return -ENODEV;

	strcpy(cgrp->root->release_agent_path, buffer);

	mutex_unlock(&cgroup_mutex);

	return 0;

}



static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,

				     struct seq_file *seq)

{

	if (!cgroup_lock_live_group(cgrp))

		return -ENODEV;

	seq_puts(seq, cgrp->root->release_agent_path);

	seq_putc(seq, '\n');

	mutex_unlock(&cgroup_mutex);

	return 0;

}



static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,

				struct file *file,

				const char __user *userbuf,
@@ -1443,10 +1478,6 @@ static ssize_t cgroup_common_file_write(struct cgroup *cgrp, 
		else

			clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

		break;

	case FILE_RELEASE_AGENT:

		BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);

		strcpy(cgrp->root->release_agent_path, buffer);

		break;

	default:

		retval = -EINVAL;

		goto out2;
@@ -1506,49 +1537,6 @@ static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft, 
	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);

}



static ssize_t cgroup_common_file_read(struct cgroup *cgrp,

					  struct cftype *cft,

					  struct file *file,

					  char __user *buf,

					  size_t nbytes, loff_t *ppos)

{

	enum cgroup_filetype type = cft->private;

	char *page;

	ssize_t retval = 0;

	char *s;



	if (!(page = (char *)__get_free_page(GFP_KERNEL)))

		return -ENOMEM;



	s = page;



	switch (type) {

	case FILE_RELEASE_AGENT:

	{

		struct cgroupfs_root *root;

		size_t n;

		mutex_lock(&cgroup_mutex);

		root = cgrp->root;

		n = strnlen(root->release_agent_path,

			    sizeof(root->release_agent_path));

		n = min(n, (size_t) PAGE_SIZE);

		strncpy(s, root->release_agent_path, n);

		mutex_unlock(&cgroup_mutex);

		s += n;

		break;

	}

	default:

		retval = -EINVAL;

		goto out;

	}

	*s++ = '\n';



	retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);

out:

	free_page((unsigned long)page);

	return retval;

}



static ssize_t cgroup_file_read(struct file *file, char __user *buf,

				   size_t nbytes, loff_t *ppos)

{
@@ -1606,6 +1594,7 @@ int cgroup_seqfile_release(struct inode *inode, struct file *file) 


static struct file_operations cgroup_seqfile_operations = {

	.read = seq_read,

	.write = cgroup_file_write,

	.llseek = seq_lseek,

	.release = cgroup_seqfile_release,

};
@@ -2283,8 +2272,9 @@ static struct cftype files[] = { 


static struct cftype cft_release_agent = {

	.name = "release_agent",

	.read = cgroup_common_file_read,

	.write = cgroup_common_file_write,

	.read_seq_string = cgroup_release_agent_show,

	.write_string = cgroup_release_agent_write,

	.max_write_len = PATH_MAX,

	.private = FILE_RELEASE_AGENT,

};
@@ -3111,27 +3101,24 @@ static void cgroup_release_agent(struct work_struct *work) 
	while (!list_empty(&release_list)) {

		char *argv[3], *envp[3];

		int i;

		char *pathbuf;

		char *pathbuf = NULL, *agentbuf = NULL;

		struct cgroup *cgrp = list_entry(release_list.next,

						    struct cgroup,

						    release_list);

		list_del_init(&cgrp->release_list);

		spin_unlock(&release_list_lock);

		pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);

		if (!pathbuf) {

			spin_lock(&release_list_lock);

			continue;

		}



		if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) {

			kfree(pathbuf);

			spin_lock(&release_list_lock);

			continue;

		}

		if (!pathbuf)

			goto continue_free;

		if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)

			goto continue_free;

		agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);

		if (!agentbuf)

			goto continue_free;



		i = 0;

		argv[i++] = cgrp->root->release_agent_path;

		argv[i++] = (char *)pathbuf;

		argv[i++] = agentbuf;

		argv[i++] = pathbuf;

		argv[i] = NULL;



		i = 0;
@@ -3145,8 +3132,10 @@ static void cgroup_release_agent(struct work_struct *work) 
		 * be a slow process */

		mutex_unlock(&cgroup_mutex);

		call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);

		kfree(pathbuf);

		mutex_lock(&cgroup_mutex);

 continue_free:

		kfree(pathbuf);

		kfree(agentbuf);

		spin_lock(&release_list_lock);

	}

	spin_unlock(&release_list_lock);

CRA Git | Maintained and supported by SUSTech CRA and CCSE