[PATCH] cgroups: fix a serious bug in cgroupstats

[Paul Menage]

On Wed, Nov 19, 2008 at 12:14 AM, Li Zefan <lizf at cn.fujitsu.com> wrote:
> 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 at linux.vnet.ibm.com>
> Signed-off-by: Li Zefan <lizf at cn.fujitsu.com>

Good catch, thanks.

Acked-by: Paul Menage <menage at google.com>



> ---
>  kernel/cgroup.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 358e775..f6f5219 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;
> --
> 1.5.4.rc3
>