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Date: Wed, 25 Sep 2013 00:17:26 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: akpm@...ux-foundation.org
Cc: oleg@...hat.com, security@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] kthread: Make kthread_create() killable.
Andrew Morton wrote:
> That's a pretty big patch. What's the status of this? Do you think
> it's ready to go? Oleg?
>
> I don't like the changelog much - it doesn't really describe the bug.
> I can google "CVE-2012-4398" and that turns up a bunch of stuff but
> it's more oriented toward sysadmins etc, rather than kernel developers.
>
> Can we please have a conventional description? When the user does A,
> the kernel does B because C, so we fix it via D?
I see. I updated description. Updated patch follows.
----------
>>From 0fe0c9d09b45cce0f00457755861204d51d7c2c9 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Wed, 25 Sep 2013 00:00:27 +0900
Subject: [PATCH] kthread: make kthread_create() killable
Any users of wait_for_completion() might be chosen by the OOM killer while
waiting for completion() call by some process which does memory
allocation. kthread_create() is one of such users.
When such users are chosen by the OOM killer when they are waiting for
completion() in TASK_UNINTERRUPTIBLE, the system will be kept stressed
due to memory starvation because the OOM killer cannot kill such users.
Fix this problem for kthreadd by making kthread_create() killable.
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
kernel/kthread.c | 73 ++++++++++++++++++++++++++++++++++++++++-------------
1 files changed, 55 insertions(+), 18 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 760e86d..b5ae3ee 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -33,7 +33,7 @@ struct kthread_create_info
/* Result passed back to kthread_create() from kthreadd. */
struct task_struct *result;
- struct completion done;
+ struct completion *done;
struct list_head list;
};
@@ -178,6 +178,7 @@ static int kthread(void *_create)
struct kthread_create_info *create = _create;
int (*threadfn)(void *data) = create->threadfn;
void *data = create->data;
+ struct completion *done;
struct kthread self;
int ret;
@@ -187,10 +188,16 @@ static int kthread(void *_create)
init_completion(&self.parked);
current->vfork_done = &self.exited;
+ /* If user was SIGKILLed, I release the structure. */
+ done = xchg(&create->done, NULL);
+ if (!done) {
+ kfree(create);
+ do_exit(-EINTR);
+ }
/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_UNINTERRUPTIBLE);
create->result = current;
- complete(&create->done);
+ complete(done);
schedule();
ret = -EINTR;
@@ -223,8 +230,15 @@ static void create_kthread(struct kthread_create_info *create)
/* We want our own signal handler (we take no signals by default). */
pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
if (pid < 0) {
+ /* If user was SIGKILLed, I release the structure. */
+ struct completion *done = xchg(&create->done, NULL);
+
+ if (!done) {
+ kfree(create);
+ return;
+ }
create->result = ERR_PTR(pid);
- complete(&create->done);
+ complete(done);
}
}
@@ -255,36 +269,59 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
const char namefmt[],
...)
{
- struct kthread_create_info create;
-
- create.threadfn = threadfn;
- create.data = data;
- create.node = node;
- init_completion(&create.done);
+ DECLARE_COMPLETION_ONSTACK(done);
+ struct task_struct *task;
+ struct kthread_create_info *create = kmalloc(sizeof(*create),
+ GFP_KERNEL);
+
+ if (!create)
+ return ERR_PTR(-ENOMEM);
+ create->threadfn = threadfn;
+ create->data = data;
+ create->node = node;
+ create->done = &done;
spin_lock(&kthread_create_lock);
- list_add_tail(&create.list, &kthread_create_list);
+ list_add_tail(&create->list, &kthread_create_list);
spin_unlock(&kthread_create_lock);
wake_up_process(kthreadd_task);
- wait_for_completion(&create.done);
-
- if (!IS_ERR(create.result)) {
+ /*
+ * Wait for completion in killable state, for I might be chosen by
+ * the OOM killer while kthreadd is trying to allocate memory for
+ * new kernel thread.
+ */
+ if (unlikely(wait_for_completion_killable(&done))) {
+ /*
+ * If I was SIGKILLed before kthreadd (or new kernel thread)
+ * calls complete(), leave the cleanup of this structure to
+ * that thread.
+ */
+ if (xchg(&create->done, NULL))
+ return ERR_PTR(-ENOMEM);
+ /*
+ * kthreadd (or new kernel thread) will call complete()
+ * shortly.
+ */
+ wait_for_completion(&done);
+ }
+ task = create->result;
+ if (!IS_ERR(task)) {
static const struct sched_param param = { .sched_priority = 0 };
va_list args;
va_start(args, namefmt);
- vsnprintf(create.result->comm, sizeof(create.result->comm),
- namefmt, args);
+ vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
va_end(args);
/*
* root may have changed our (kthreadd's) priority or CPU mask.
* The kernel thread should not inherit these properties.
*/
- sched_setscheduler_nocheck(create.result, SCHED_NORMAL, ¶m);
- set_cpus_allowed_ptr(create.result, cpu_all_mask);
+ sched_setscheduler_nocheck(task, SCHED_NORMAL, ¶m);
+ set_cpus_allowed_ptr(task, cpu_all_mask);
}
- return create.result;
+ kfree(create);
+ return task;
}
EXPORT_SYMBOL(kthread_create_on_node);
--
1.7.1
--
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