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Message-ID: <20130125072633.GD4503@ZenIV.linux.org.uk>
Date: Fri, 25 Jan 2013 07:26:33 +0000
From: Al Viro <viro@...IV.linux.org.uk>
To: Li Zefan <lizefan@...wei.com>
Cc: Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>,
David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename()
race
On Fri, Jan 25, 2013 at 03:09:48PM +0800, Li Zefan wrote:
> 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.
>
> Signed-off-by: Li Zefan <lizefan@...wei.com>
> ---
> kernel/cpuset.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 16be7c9..b2476c2 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -2606,8 +2606,12 @@ void cpuset_print_task_mems_allowed(struct task_struct *tsk)
>
> dentry = task_cs(tsk)->css.cgroup->dentry;
> spin_lock(&cpuset_buffer_lock);
> +
> + spin_lock(&dentry->d_lock);
> snprintf(cpuset_name, CPUSET_NAME_LEN,
> dentry ? (const char *)dentry->d_name.name : "/");
Ahem... Can dentry actually be NULL here? If not, this conditional
is bogus; otherwise, spin_lock(&dentry->d_lock) is going to blow up...
--
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