* [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[parent not found: <51022FBC.2020705-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]
* 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
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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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