* [PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race
@ 2013-01-25 7:09 Li Zefan
[not found] ` <51022FBC.2020705-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
0 siblings, 1 reply; 3+ messages in thread
From: Li Zefan @ 2013-01-25 7:09 UTC (permalink / raw)
To: Tejun Heo; +Cc: LKML, Cgroups, David Rientjes, Al Viro
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-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
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 : "/");
+ 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",
--
1.8.0.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race
[not found] ` <51022FBC.2020705-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
@ 2013-01-25 7:26 ` Al Viro
2013-01-25 7:29 ` Li Zefan
0 siblings, 1 reply; 3+ messages in thread
From: Al Viro @ 2013-01-25 7:26 UTC (permalink / raw)
To: Li Zefan; +Cc: Tejun Heo, LKML, Cgroups, David Rientjes
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-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> ---
> 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...
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race
2013-01-25 7:26 ` Al Viro
@ 2013-01-25 7:29 ` Li Zefan
0 siblings, 0 replies; 3+ messages in thread
From: Li Zefan @ 2013-01-25 7:29 UTC (permalink / raw)
To: Al Viro; +Cc: Tejun Heo, LKML, Cgroups, David Rientjes
On 2013/1/25 15:26, Al Viro wrpte:
> 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@huawei.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...
oops, my fault...It's NULL if cpuset is not mounted.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2013-01-25 7:29 UTC | newest]
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2013-01-25 7:09 [PATCH] cpuset: fix cpuset_print_task_mems_allowed() vs rename() race Li Zefan
[not found] ` <51022FBC.2020705-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2013-01-25 7:26 ` Al Viro
2013-01-25 7:29 ` Li Zefan
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