[patch 008/104] cgroups: fix a serious bug in cgroupstats

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Li Zefan <lizf@xxxxxxxxxxxxxx>

commit 33d283bef23132c48195eafc21449f8ba88fce6b upstream.

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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
Acked-by: Paul Menage <menage@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/cgroup.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2045,10 +2045,13 @@ int cgroupstats_build(struct cgroupstats
 	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;

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