cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

commit 63f43f55c9bbc14f76b582644019b8a07dc8219a upstream.

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>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 84a524b..835eee6 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2507,8 +2507,16 @@ 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",