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Old 07-07-2011, 11:17 AM
Andy Whitcroft
Default taskstats: don't allow duplicate entries in listener mode

From: Vasiliy Kulikov <segoon@openwall.com>

Currently a single process may register exit handlers unlimited times.
It may lead to a bloated listeners chain and very slow process

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>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit 26c4caea9d697043cc5a458b96411b86d7f6babd)
BugLink: http://bugs.launchpad.net/bugs/806390
Signed-off-by: Andy Whitcroft <apw@canonical.com>
kernel/taskstats.c | 15 ++++++++++++---
1 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index ea8384d..b080920 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -293,16 +293,18 @@ 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;
@@ -311,9 +313,16 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)

listeners = &per_cpu(listener_array, cpu);
+ 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;
+ kfree(s);
return 0;


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