[PATCH v2] task_work: kasan: record task_work_add() call stack

[PATCH v2] task_work: kasan: record task_work_add() call stack

[Walter Wu]

Why record task_work_add() call stack?
Syzbot reports many use-after-free issues for task_work, see [1].
After see the free stack and the current auxiliary stack, we think
they are useless, we don't know where register the work, this work
may be the free call stack, so that we miss the root cause and
don't solve the use-after-free.

Add task_work_add() call stack into KASAN auxiliary stack in
order to improve KASAN report. It is useful for programmers
to solve use-after-free issues.

[1]: https://groups.google.com/g/syzkaller-bugs/search?q=kasan%20use-after-free%20task_work_run

Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Oleg Nesterov <oleg@redhat.com>
---

v2: Fix kasan_record_aux_stack() calling sequence issue.
    Thanks for Dmitry's suggestion

---
 kernel/task_work.c | 3 +++
 mm/kasan/kasan.h   | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 9cde961875c0..3d4852891fa8 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 {
 	struct callback_head *head;
 
+	/* record the work call stack in order to print it in KASAN reports */
+	kasan_record_aux_stack(work);
+
 	do {
 		head = READ_ONCE(task->task_works);
 		if (unlikely(head == &work_exited))
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3436c6bf7c0c..e4629a971a3c 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -146,7 +146,7 @@ struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
 #ifdef CONFIG_KASAN_GENERIC
 	/*
-	 * call_rcu() call stack is stored into struct kasan_alloc_meta.
+	 * The auxiliary stack is stored into struct kasan_alloc_meta.
 	 * The free stack is stored into struct kasan_free_meta.
 	 */
 	depot_stack_handle_t aux_stack[2];
-- 
2.18.0

Re: [PATCH v2] task_work: kasan: record task_work_add() call stack

[Dmitry Vyukov]

On Tue, Mar 16, 2021 at 3:44 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> Why record task_work_add() call stack?
> Syzbot reports many use-after-free issues for task_work, see [1].
> After see the free stack and the current auxiliary stack, we think
> they are useless, we don't know where register the work, this work
> may be the free call stack, so that we miss the root cause and
> don't solve the use-after-free.
>
> Add task_work_add() call stack into KASAN auxiliary stack in
> order to improve KASAN report. It is useful for programmers
> to solve use-after-free issues.
>
> [1]: https://groups.google.com/g/syzkaller-bugs/search?q=kasan%20use-after-free%20task_work_run
>
> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Oleg Nesterov <oleg@redhat.com>
> ---
>
> v2: Fix kasan_record_aux_stack() calling sequence issue.
>     Thanks for Dmitry's suggestion

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

> ---
>  kernel/task_work.c | 3 +++
>  mm/kasan/kasan.h   | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 9cde961875c0..3d4852891fa8 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
>  {
>         struct callback_head *head;
>
> +       /* record the work call stack in order to print it in KASAN reports */
> +       kasan_record_aux_stack(work);
> +
>         do {
>                 head = READ_ONCE(task->task_works);
>                 if (unlikely(head == &work_exited))
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 3436c6bf7c0c..e4629a971a3c 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -146,7 +146,7 @@ struct kasan_alloc_meta {
>         struct kasan_track alloc_track;
>  #ifdef CONFIG_KASAN_GENERIC
>         /*
> -        * call_rcu() call stack is stored into struct kasan_alloc_meta.
> +        * The auxiliary stack is stored into struct kasan_alloc_meta.
>          * The free stack is stored into struct kasan_free_meta.
>          */
>         depot_stack_handle_t aux_stack[2];
> --
> 2.18.0
>
> --
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Re: [PATCH v2] task_work: kasan: record task_work_add() call stack

[Jens Axboe]

On 3/15/21 8:44 PM, Walter Wu wrote:
> Why record task_work_add() call stack?
> Syzbot reports many use-after-free issues for task_work, see [1].
> After see the free stack and the current auxiliary stack, we think
> they are useless, we don't know where register the work, this work
> may be the free call stack, so that we miss the root cause and
> don't solve the use-after-free.
> 
> Add task_work_add() call stack into KASAN auxiliary stack in
> order to improve KASAN report. It is useful for programmers
> to solve use-after-free issues.

I think this is a very useful addition, especially as task_work
proliferates.

Reviewed-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe

Re: [PATCH v2] task_work: kasan: record task_work_add() call stack

[Oleg Nesterov]

On 03/16, Walter Wu wrote:
>
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
>  {
>  	struct callback_head *head;
>
> +	/* record the work call stack in order to print it in KASAN reports */
> +	kasan_record_aux_stack(work);
> +
>  	do {
>  		head = READ_ONCE(task->task_works);
>  		if (unlikely(head == &work_exited))

Acked-by: Oleg Nesterov <oleg@redhat.com>

Re: [PATCH v2] task_work: kasan: record task_work_add() call stack

[Andrey Konovalov]

On Tue, Mar 16, 2021 at 3:44 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> Why record task_work_add() call stack?
> Syzbot reports many use-after-free issues for task_work, see [1].
> After see the free stack and the current auxiliary stack, we think
> they are useless, we don't know where register the work, this work
> may be the free call stack, so that we miss the root cause and
> don't solve the use-after-free.
>
> Add task_work_add() call stack into KASAN auxiliary stack in
> order to improve KASAN report. It is useful for programmers
> to solve use-after-free issues.
>
> [1]: https://groups.google.com/g/syzkaller-bugs/search?q=kasan%20use-after-free%20task_work_run
>
> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Oleg Nesterov <oleg@redhat.com>
> ---
>
> v2: Fix kasan_record_aux_stack() calling sequence issue.
>     Thanks for Dmitry's suggestion
>
> ---
>  kernel/task_work.c | 3 +++
>  mm/kasan/kasan.h   | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 9cde961875c0..3d4852891fa8 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
>  {
>         struct callback_head *head;
>
> +       /* record the work call stack in order to print it in KASAN reports */
> +       kasan_record_aux_stack(work);
> +
>         do {
>                 head = READ_ONCE(task->task_works);
>                 if (unlikely(head == &work_exited))
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 3436c6bf7c0c..e4629a971a3c 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -146,7 +146,7 @@ struct kasan_alloc_meta {
>         struct kasan_track alloc_track;
>  #ifdef CONFIG_KASAN_GENERIC
>         /*
> -        * call_rcu() call stack is stored into struct kasan_alloc_meta.
> +        * The auxiliary stack is stored into struct kasan_alloc_meta.
>          * The free stack is stored into struct kasan_free_meta.
>          */
>         depot_stack_handle_t aux_stack[2];
> --

Acked-by: Andrey Konovalov <andreyknvl@google.com>