[PATCH v2] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

[PATCH v2] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

[Li Zefan]

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.

It's safe in the protection of dentry->d_lock.

v2: check NULL dentry before acquiring dentry lock.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 kernel/cpuset.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 16be7c9..4f9dfe4 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2606,8 +2606,16 @@ void cpuset_print_task_mems_allowed(struct task_struct *tsk)
 
 	dentry = task_cs(tsk)->css.cgroup->dentry;
 	spin_lock(&cpuset_buffer_lock);
-	snprintf(cpuset_name, CPUSET_NAME_LEN,
-		 dentry ? (const char *)dentry->d_name.name : "/");
+
+	if (!dentry) {
+		strcpy(cpuset_name, "/");
+	} else {
+		spin_lock(&dentry->d_lock);
+		strlcpy(cpuset_name, (const char *)dentry->d_name.name,
+			CPUSET_NAME_LEN);
+		spin_unlock(&dentry->d_lock);
+	}
+
 	nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
 			   tsk->mems_allowed);
 	printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
-- 
1.8.0.2

Re: [PATCH v2] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

[Tejun Heo]

On Fri, Jan 25, 2013 at 04:08:01PM +0800, Li Zefan wrote:
> 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.
> 
> It's safe in the protection of dentry->d_lock.
> 
> v2: check NULL dentry before acquiring dentry lock.
> 
> Signed-off-by: Li Zefan <lizefan@huawei.com>

Applied to cgroup/for-3.8-fixes w/ stable cc'd.

Thanks.

-- 
tejun