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

CVE-2011-2484
The add_del_listener function in kernel/taskstats.c in the Linux
kernel 2.6.39.1 and earlier does not prevent multiple registrations
of exit handlers, which allows local users to cause a denial of
service (memory and CPU consumption), and bypass the OOM Killer,
via a crafted application.

The fix for this issue has already hit oneiric via upstream. Following
this email are two patches, one a backport for hardy, and the other a
clean cherry-pick of the upstream commit for lucid, lucid/fsl-imx51,
maverick, maverick/ti-omap4, natty, and natty/ti-omap4.

Proposing for SRU to hardy, lucid, lucid/fsl-imx51, maverick,
maverick/ti-omap4, natty, and natty/ti-omap4.

-apw

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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
terminations.

Eg 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>
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>

(backported from commit 26c4caea9d697043cc5a458b96411b86d7f6babd)
CVE-2011-2484
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 07e86a8..99e20d1 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -293,17 +293,19 @@ ret:
static int add_del_listener(pid_t pid, cpumask_t *maskp, int isadd)
{
struct listener_list *listeners;
- struct listener *s, *tmp;
+ struct listener *s, *tmp, *s2;
unsigned int cpu;
cpumask_t mask = *maskp;

if (!cpus_subset(mask, cpu_possible_map))
return -EINVAL;

+ s = NULL;
if (isadd == REGISTER) {
for_each_cpu_mask(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;
@@ -312,9 +314,16 @@ static int add_del_listener(pid_t pid, cpumask_t *maskp, 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;
}

--
1.7.4.1


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