[PATCH v2] taskstats: don't allow duplicate entries in listener mode

[PATCH v2] taskstats: don't allow duplicate entries in listener mode

[Vasiliy Kulikov]

Currently a single process may register exit handlers unlimited times.
It may lead to a bloated listeners chain and very slow process terminations.
E.g. after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of
kernel memory is stolen for the handlers chain and "time id" shows 2-7
seconds instead of normal 0.003.  It makes it possible to exhaust all
kernel memory and to eat much of CPU time by triggerring numerous exits
on a single CPU.

The patch limits the number of times a single process may register
itself on a single CPU to one.

One little issue is kept unfixed - as taskstats_exit() is called before
exit_files() in do_exit(), the orphaned listener entry (if it was not
explicitly deregistered) is kept until the next someone's exit() and
implicit deregistration in send_cpu_listeners().  So, if a process
registered itself as a listener exits and the next spawned process gets
the same pid, it would inherit taskstats attributes.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
---
 v2 - removed wrong "From" line.

 kernel/taskstats.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 9ffea36..fc0f220 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -285,16 +285,18 @@ ret:
 static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
 {
 	struct listener_list *listeners;
-	struct listener *s, *tmp;
+	struct listener *s, *tmp, *s2;
 	unsigned int cpu;
 
 	if (!cpumask_subset(mask, cpu_possible_mask))
 		return -EINVAL;
 
+	s = NULL;
 	if (isadd == REGISTER) {
 		for_each_cpu(cpu, mask) {
-			s = kmalloc_node(sizeof(struct listener), GFP_KERNEL,
-					 cpu_to_node(cpu));
+			if (!s)
+				s = kmalloc_node(sizeof(struct listener),
+						 GFP_KERNEL, cpu_to_node(cpu));
 			if (!s)
 				goto cleanup;
 			s->pid = pid;
@@ -303,9 +305,16 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
 
 			listeners = &per_cpu(listener_array, cpu);
 			down_write(&listeners->sem);
+			list_for_each_entry_safe(s2, tmp, &listeners->list, list) {
+				if (s2->pid == pid)
+					goto next_cpu;
+			}
 			list_add(&s->list, &listeners->list);
+			s = NULL;
+next_cpu:
 			up_write(&listeners->sem);
 		}
+		kfree(s);
 		return 0;
 	}
 
-- 
1.7.0.4

Re: [PATCH v2] taskstats: don't allow duplicate entries in listener mode

[Andrew Morton]

On Thu, 16 Jun 2011 19:55:59 +0400
Vasiliy Kulikov <segoon@openwall.com> wrote:

> Currently a single process may register exit handlers unlimited times.
> It may lead to a bloated listeners chain and very slow process terminations.
> E.g. after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of
> kernel memory is stolen for the handlers chain and "time id" shows 2-7
> seconds instead of normal 0.003.  It makes it possible to exhaust all
> kernel memory and to eat much of CPU time by triggerring numerous exits
> on a single CPU.
> 
> The patch limits the number of times a single process may register
> itself on a single CPU to one.
> 
> One little issue is kept unfixed - as taskstats_exit() is called before
> exit_files() in do_exit(), the orphaned listener entry (if it was not
> explicitly deregistered) is kept until the next someone's exit() and
> implicit deregistration in send_cpu_listeners().  So, if a process
> registered itself as a listener exits and the next spawned process gets
> the same pid, it would inherit taskstats attributes.

ow. That's an unprivileged operation, isn't it?

> 
> diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> index 9ffea36..fc0f220 100644
> --- a/kernel/taskstats.c
> +++ b/kernel/taskstats.c
> @@ -285,16 +285,18 @@ ret:
>  static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
>  {
>  	struct listener_list *listeners;
> -	struct listener *s, *tmp;
> +	struct listener *s, *tmp, *s2;
>  	unsigned int cpu;
>  
>  	if (!cpumask_subset(mask, cpu_possible_mask))
>  		return -EINVAL;
>  
> +	s = NULL;
>  	if (isadd == REGISTER) {
>  		for_each_cpu(cpu, mask) {
> -			s = kmalloc_node(sizeof(struct listener), GFP_KERNEL,
> -					 cpu_to_node(cpu));
> +			if (!s)
> +				s = kmalloc_node(sizeof(struct listener),
> +						 GFP_KERNEL, cpu_to_node(cpu));
>  			if (!s)
>  				goto cleanup;
>  			s->pid = pid;
> @@ -303,9 +305,16 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
>  
>  			listeners = &per_cpu(listener_array, cpu);
>  			down_write(&listeners->sem);
> +			list_for_each_entry_safe(s2, tmp, &listeners->list, list) {
> +				if (s2->pid == pid)
> +					goto next_cpu;
> +			}
>  			list_add(&s->list, &listeners->list);
> +			s = NULL;
> +next_cpu:
>  			up_write(&listeners->sem);
>  		}
> +		kfree(s);
>  		return 0;
>  	}
>  

Re: [PATCH v2] taskstats: don't allow duplicate entries in listener mode

[Vasiliy Kulikov]

On Tue, Jun 21, 2011 at 15:49 -0700, Andrew Morton wrote:
> On Thu, 16 Jun 2011 19:55:59 +0400
> Vasiliy Kulikov <segoon@openwall.com> wrote:
> 
> > Currently a single process may register exit handlers unlimited times.
> > It may lead to a bloated listeners chain and very slow process terminations.
> > E.g. after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of
> > kernel memory is stolen for the handlers chain and "time id" shows 2-7
> > seconds instead of normal 0.003.  It makes it possible to exhaust all
> > kernel memory and to eat much of CPU time by triggerring numerous exits
> > on a single CPU.
> > 
> > The patch limits the number of times a single process may register
> > itself on a single CPU to one.
> > 
> > One little issue is kept unfixed - as taskstats_exit() is called before
> > exit_files() in do_exit(), the orphaned listener entry (if it was not
> > explicitly deregistered) is kept until the next someone's exit() and
> > implicit deregistration in send_cpu_listeners().  So, if a process
> > registered itself as a listener exits and the next spawned process gets
> > the same pid, it would inherit taskstats attributes.
> 
> ow. That's an unprivileged operation, isn't it?

Yes.


Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments