[ 62/77] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race

From: Greg Kroah-Hartman
Date: Fri Mar 01 2013 - 15:12:31 EST


3.8-stable review patch. If anyone has any objections, please let me know.

------------------

From: Li Zefan <lizefan@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/cpuset.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2511,8 +2511,16 @@ void cpuset_print_task_mems_allowed(stru

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",


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