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Message-ID: <51205699.5080900@huawei.com>
Date: Sun, 17 Feb 2013 12:03:37 +0800
From: Li Zefan <lizefan@...wei.com>
To: Tejun Heo <tj@...nel.org>
CC: LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>,
Sasha Levin <levinsasha928@...il.com>,
Al Viro <viro@...IV.linux.org.uk>
Subject: [PATCH 2/2] cgroup: fix cgroup_path() vs rename() race, take 2
rename() will change dentry->d_name. The result of this race can
be worse than seeing partially rewritten name, but we might access
a stale pointer because rename() will re-allocate memory to hold
a longer name.
As accessing dentry->name must be protected by dentry->d_lock or
parent inode's i_mutex, while on the other hand cgroup-path() can
be called with some irq-safe spinlocks held, we can't generate
cgroup path using dentry->d_name.
Alternatively we make a copy of dentry->d_lock and save it in
cgrp->name when a cgroup is created, and update cgrp->name at
rename().
Signed-off-by: Li Zefan <lizefan@...wei.com>
---
include/linux/cgroup.h | 4 ++-
kernel/cgroup.c | 94 +++++++++++++++++++++++++++++++++++++++-----------
2 files changed, 76 insertions(+), 22 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 900af59..8b2ce2a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -171,6 +171,8 @@ struct cgroup {
struct cgroup *parent; /* my parent */
struct dentry *dentry; /* cgroup fs entry, RCU protected */
+ char *name; /* a copy of dentry->d_name */
+ spinlock_t name_lock;
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
@@ -409,7 +411,7 @@ int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_is_removed(const struct cgroup *cgrp);
-int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
+int cgroup_path(struct cgroup *cgrp, char *buf, int buflen);
int cgroup_task_count(const struct cgroup *cgrp);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5d4c92e..cea6a88 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -890,6 +890,7 @@ static void cgroup_free_fn(struct work_struct *work)
simple_xattrs_free(&cgrp->xattrs);
ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
+ kfree(cgrp->name);
kfree(cgrp);
}
@@ -1410,6 +1411,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
mutex_init(&cgrp->pidlist_mutex);
INIT_LIST_HEAD(&cgrp->event_list);
spin_lock_init(&cgrp->event_list_lock);
+ spin_lock_init(&cgrp->name_lock);
simple_xattrs_init(&cgrp->xattrs);
}
@@ -1565,6 +1567,18 @@ static int cgroup_get_rootdir(struct super_block *sb)
return 0;
}
+static char *cgroup_alloc_name(struct dentry *dentry)
+{
+ char *name;
+
+ name = kmalloc(dentry->d_name.len + 1, GFP_KERNEL);
+ if (!name)
+ return NULL;
+ memcpy(name, dentry->d_name.name, dentry->d_name.len);
+ name[dentry->d_name.len] = '\0';
+ return name;
+}
+
static struct dentry *cgroup_mount(struct file_system_type *fs_type,
int flags, const char *unused_dev_name,
void *data)
@@ -1613,13 +1627,19 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
int i;
struct hlist_node *node;
struct css_set *cg;
+ struct dentry *dentry;
BUG_ON(sb->s_root != NULL);
ret = cgroup_get_rootdir(sb);
if (ret)
goto drop_new_super;
- inode = sb->s_root->d_inode;
+ dentry = sb->s_root;
+ inode = dentry->d_inode;
+
+ root_cgrp->name = cgroup_alloc_name(dentry);
+ if (!root_cgrp->name)
+ goto drop_new_super;
mutex_lock(&inode->i_mutex);
mutex_lock(&cgroup_mutex);
@@ -1660,8 +1680,8 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
list_add(&root->root_list, &roots);
root_count++;
- sb->s_root->d_fsdata = root_cgrp;
- root->top_cgroup.dentry = sb->s_root;
+ dentry->d_fsdata = root_cgrp;
+ root->top_cgroup.dentry = dentry;
/* Link the top cgroup in this hierarchy into all
* the css_set objects */
@@ -1751,6 +1771,7 @@ static void cgroup_kill_sb(struct super_block *sb) {
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
+ kfree(cgrp->name);
simple_xattrs_free(&cgrp->xattrs);
kill_litter_super(sb);
@@ -1774,38 +1795,39 @@ static struct kobject *cgroup_kobj;
* Called with cgroup_mutex held or else with an RCU-protected cgroup
* reference. Writes path of cgroup into buf. Returns 0 on success,
* -errno on error.
+ *
+ * We can't generate cgroup path using dentry->d_name, as accessing
+ * dentry->name must be protected by irq-unsafe dentry->d_lock or
+ * parent inode's i_mutex, while on the other hand cgroup_path() can
+ * be called with some irq-safe spinlocks held.
*/
-int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
+int cgroup_path(struct cgroup *cgrp, char *buf, int buflen)
{
- struct dentry *dentry = cgrp->dentry;
char *start;
rcu_lockdep_assert(rcu_read_lock_held() || cgroup_lock_is_held(),
"cgroup_path() called without proper locking");
- if (cgrp == dummytop) {
- /*
- * Inactive subsystems have no dentry for their root
- * cgroup
- */
- strcpy(buf, "/");
- return 0;
- }
-
start = buf + buflen - 1;
*start = '\0';
- for (;;) {
- int len = dentry->d_name.len;
+ while (true) {
+ int len;
+ unsigned long flags;
- if ((start -= len) < buf)
+ spin_lock_irqsave(&cgrp->name_lock, flags);
+ len = strlen(cgrp->name);
+ if ((start -= len) < buf) {
+ spin_unlock_irqrestore(&cgrp->name_lock, flags);
return -ENAMETOOLONG;
- memcpy(start, dentry->d_name.name, len);
+ }
+ memcpy(start, cgrp->name, len);
+ spin_unlock_irqrestore(&cgrp->name_lock, flags);
+
cgrp = cgrp->parent;
if (!cgrp)
break;
- dentry = cgrp->dentry;
if (!cgrp->parent)
continue;
if (--start < buf)
@@ -2539,13 +2561,35 @@ static int cgroup_file_release(struct inode *inode, struct file *file)
static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
struct inode *new_dir, struct dentry *new_dentry)
{
+ unsigned long flags;
+ int ret;
+ char *name;
+ struct cgroup *cgrp;
+
if (!S_ISDIR(old_dentry->d_inode->i_mode))
return -ENOTDIR;
if (new_dentry->d_inode)
return -EEXIST;
if (old_dir != new_dir)
return -EIO;
- return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+
+ cgrp = __d_cgrp(old_dentry);
+
+ name = cgroup_alloc_name(new_dentry);
+ if (!name)
+ return -ENOMEM;
+
+ ret = simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+ if (ret) {
+ kfree(name);
+ return ret;
+ }
+
+ spin_lock_irqsave(&cgrp->name_lock, flags);
+ kfree(cgrp->name);
+ cgrp->name = name;
+ spin_unlock_irqrestore(&cgrp->name_lock, flags);
+ return 0;
}
static struct simple_xattrs *__d_xattrs(struct dentry *dentry)
@@ -4144,9 +4188,13 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (!cgrp)
return -ENOMEM;
+ cgrp->name = cgroup_alloc_name(dentry);
+ if (!cgrp->name)
+ goto err_free_cgrp;
+
cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
if (cgrp->id < 0)
- goto err_free_cgrp;
+ goto err_free_name;
/*
* Only live parents can have children. Note that the liveliness
@@ -4252,6 +4300,8 @@ err_free_all:
deactivate_super(sb);
err_free_id:
ida_simple_remove(&root->cgroup_ida, cgrp->id);
+err_free_name:
+ kfree(cgrp->name);
err_free_cgrp:
kfree(cgrp);
return err;
@@ -4656,6 +4706,8 @@ int __init cgroup_init_early(void)
root_count = 1;
init_task.cgroups = &init_css_set;
+ dummytop->name = "/";
+
init_css_set_link.cg = &init_css_set;
init_css_set_link.cgrp = dummytop;
list_add(&init_css_set_link.cgrp_link_list,
--
1.8.0.2
--
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