cgroups: fix a serious bug in cgroupstats

Try this, and you'll get oops immediately:
 # cd Documentation/accounting/
 # gcc -o getdelays getdelays.c
 # mount -t cgroup -o debug xxx /mnt
 # ./getdelays -C /mnt/tasks

Because a normal file's dentry->d_fsdata is a pointer to struct cftype,
not struct cgroup.

After the patch, it returns EINVAL if we try to get cgroupstats
from a normal file.

Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Cc: <stable@kernel.org>		[2.6.25.x, 2.6.26.x, 2.6.27.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1a06be61dcd0..fe00b3b983a8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2039,10 +2039,13 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
         struct cgroup *cgrp;
         struct cgroup_iter it;
         struct task_struct *tsk;
+
         /*
-         * Validate dentry by checking the superblock operations
+         * Validate dentry by checking the superblock operations,
+         * and make sure it's a directory.
          */
-        if (dentry->d_sb->s_op != &cgroup_ops)
+        if (dentry->d_sb->s_op != &cgroup_ops ||
+            !S_ISDIR(dentry->d_inode->i_mode))
                  goto err;
 
         ret = 0;