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: Paul 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: Serge Hallyn <serue@us.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul Menage
Linus Torvalds
Родитель
db3b14978a
Коммит
e788e066c6
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@ -295,6 +295,8 @@ int cgroup_add_files(struct cgroup *cgrp,
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int cgroup_is_removed(const struct cgroup *cgrp);
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int cgroup_lock_live_group(struct cgroup *cgrp);
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int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
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int cgroup_task_count(const struct cgroup *cgrp);
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125
kernel/cgroup.c
125
kernel/cgroup.c
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@ -89,11 +89,7 @@ struct cgroupfs_root {
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/* Hierarchy-specific flags */
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unsigned long flags;
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/* The path to use for release notifications. No locking
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* between setting and use - so if userspace updates this
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* while child cgroups exist, you could miss a
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* notification. We ensure that it's always a valid
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* NUL-terminated string */
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/* The path to use for release notifications. */
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char release_agent_path[PATH_MAX];
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};
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@ -1329,6 +1325,45 @@ enum cgroup_filetype {
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FILE_RELEASE_AGENT,
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};
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/**
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* cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
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* @cgrp: the cgroup to be checked for liveness
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*
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* Returns true (with lock held) on success, or false (with no lock
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* held) on failure.
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*/
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int cgroup_lock_live_group(struct cgroup *cgrp)
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{
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mutex_lock(&cgroup_mutex);
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if (cgroup_is_removed(cgrp)) {
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mutex_unlock(&cgroup_mutex);
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return false;
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}
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return true;
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}
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static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
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const char *buffer)
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{
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BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
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if (!cgroup_lock_live_group(cgrp))
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return -ENODEV;
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strcpy(cgrp->root->release_agent_path, buffer);
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mutex_unlock(&cgroup_mutex);
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return 0;
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}
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static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
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struct seq_file *seq)
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{
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if (!cgroup_lock_live_group(cgrp))
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return -ENODEV;
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seq_puts(seq, cgrp->root->release_agent_path);
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seq_putc(seq, '\n');
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mutex_unlock(&cgroup_mutex);
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return 0;
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}
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static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
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struct file *file,
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const char __user *userbuf,
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@ -1443,10 +1478,6 @@ static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
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else
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clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
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break;
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case FILE_RELEASE_AGENT:
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BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
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strcpy(cgrp->root->release_agent_path, buffer);
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break;
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default:
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retval = -EINVAL;
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goto out2;
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@ -1506,49 +1537,6 @@ static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
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return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
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}
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static ssize_t cgroup_common_file_read(struct cgroup *cgrp,
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struct cftype *cft,
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struct file *file,
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char __user *buf,
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size_t nbytes, loff_t *ppos)
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{
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enum cgroup_filetype type = cft->private;
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char *page;
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ssize_t retval = 0;
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char *s;
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if (!(page = (char *)__get_free_page(GFP_KERNEL)))
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return -ENOMEM;
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s = page;
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switch (type) {
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case FILE_RELEASE_AGENT:
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{
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struct cgroupfs_root *root;
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size_t n;
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mutex_lock(&cgroup_mutex);
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root = cgrp->root;
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n = strnlen(root->release_agent_path,
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sizeof(root->release_agent_path));
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n = min(n, (size_t) PAGE_SIZE);
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strncpy(s, root->release_agent_path, n);
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mutex_unlock(&cgroup_mutex);
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s += n;
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break;
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}
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default:
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retval = -EINVAL;
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goto out;
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}
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*s++ = '\n';
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retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
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out:
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free_page((unsigned long)page);
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return retval;
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}
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static ssize_t cgroup_file_read(struct file *file, char __user *buf,
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size_t nbytes, loff_t *ppos)
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{
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@ -1606,6 +1594,7 @@ int cgroup_seqfile_release(struct inode *inode, struct file *file)
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static struct file_operations cgroup_seqfile_operations = {
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.read = seq_read,
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.write = cgroup_file_write,
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.llseek = seq_lseek,
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.release = cgroup_seqfile_release,
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};
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@ -2283,8 +2272,9 @@ static struct cftype files[] = {
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static struct cftype cft_release_agent = {
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.name = "release_agent",
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.read = cgroup_common_file_read,
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.write = cgroup_common_file_write,
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.read_seq_string = cgroup_release_agent_show,
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.write_string = cgroup_release_agent_write,
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.max_write_len = PATH_MAX,
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.private = FILE_RELEASE_AGENT,
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};
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@ -3111,27 +3101,24 @@ static void cgroup_release_agent(struct work_struct *work)
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while (!list_empty(&release_list)) {
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char *argv[3], *envp[3];
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int i;
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char *pathbuf;
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char *pathbuf = NULL, *agentbuf = NULL;
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struct cgroup *cgrp = list_entry(release_list.next,
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struct cgroup,
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release_list);
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list_del_init(&cgrp->release_list);
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spin_unlock(&release_list_lock);
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pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
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if (!pathbuf) {
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spin_lock(&release_list_lock);
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continue;
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}
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if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) {
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kfree(pathbuf);
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spin_lock(&release_list_lock);
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continue;
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}
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if (!pathbuf)
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goto continue_free;
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if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
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goto continue_free;
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agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
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if (!agentbuf)
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goto continue_free;
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i = 0;
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argv[i++] = cgrp->root->release_agent_path;
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argv[i++] = (char *)pathbuf;
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argv[i++] = agentbuf;
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argv[i++] = pathbuf;
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argv[i] = NULL;
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i = 0;
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@ -3145,8 +3132,10 @@ static void cgroup_release_agent(struct work_struct *work)
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* be a slow process */
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mutex_unlock(&cgroup_mutex);
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call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
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kfree(pathbuf);
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mutex_lock(&cgroup_mutex);
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continue_free:
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kfree(pathbuf);
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kfree(agentbuf);
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spin_lock(&release_list_lock);
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}
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spin_unlock(&release_list_lock);
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