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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3a99cc2..0120b5d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -89,11 +89,7 @@
/* 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 @@
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 @@
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 @@
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 @@
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 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 @@
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 @@
* 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);