[v2] binder: Don't use mmput() from shrinker function.
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Message ID 4ba9adb2-43f5-2de0-22de-f6075c1fab50@i-love.sakura.ne.jp
State New
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Series
  • [v2] binder: Don't use mmput() from shrinker function.
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Commit Message

Tetsuo Handa July 16, 2020, 3:12 p.m. UTC
syzbot is reporting that mmput() from shrinker function has a risk of
deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.

Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
callback") replaced mmput() with mmput_async() in order to avoid sleeping
with spinlock held. But this patch replaces mmput() with mmput_async() in
order not to start __mmput() from shrinker context.

[1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45

Reported-by: syzbot <syzbot+1068f09c44d151250c33@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+e5344baa319c9a96edec@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 drivers/android/binder_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Michal Hocko July 16, 2020, 3:17 p.m. UTC | #1
On Fri 17-07-20 00:12:15, Tetsuo Handa wrote:
> syzbot is reporting that mmput() from shrinker function has a risk of
> deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
> kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
> uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
> 
> Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
> callback") replaced mmput() with mmput_async() in order to avoid sleeping
> with spinlock held. But this patch replaces mmput() with mmput_async() in
> order not to start __mmput() from shrinker context.
> 
> [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
> 
> Reported-by: syzbot <syzbot+1068f09c44d151250c33@syzkaller.appspotmail.com>
> Reported-by: syzbot <syzbot+e5344baa319c9a96edec@syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Reviewed-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  drivers/android/binder_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 42c672f1584e..cbe6aa77d50d 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -947,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
>  		trace_binder_unmap_user_end(alloc, index);
>  	}
>  	mmap_read_unlock(mm);
> -	mmput(mm);
> +	mmput_async(mm);
>  
>  	trace_binder_unmap_kernel_start(alloc, index);
>  
> -- 
> 2.18.4
Christian Brauner July 16, 2020, 4:29 p.m. UTC | #2
On Thu, Jul 16, 2020 at 05:17:56PM +0200, Michal Hocko wrote:
> On Fri 17-07-20 00:12:15, Tetsuo Handa wrote:
> > syzbot is reporting that mmput() from shrinker function has a risk of
> > deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
> > kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
> > uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
> > 
> > Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
> > callback") replaced mmput() with mmput_async() in order to avoid sleeping
> > with spinlock held. But this patch replaces mmput() with mmput_async() in
> > order not to start __mmput() from shrinker context.
> > 
> > [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
> > 
> > Reported-by: syzbot <syzbot+1068f09c44d151250c33@syzkaller.appspotmail.com>
> > Reported-by: syzbot <syzbot+e5344baa319c9a96edec@syzkaller.appspotmail.com>
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> 
> Reviewed-by: Michal Hocko <mhocko@suse.com>

Thanks for the careful review Michal!
Does this need a Cc: stable?

Otherwise

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Thanks!
Christian
Tetsuo Handa July 16, 2020, 10:27 p.m. UTC | #3
On 2020/07/17 1:29, Christian Brauner wrote:
> Does this need a Cc: stable?

Up to someone who applies this patch. I think this race is hard to hit.
Todd Kjos July 16, 2020, 11:53 p.m. UTC | #4
On Thu, Jul 16, 2020 at 8:18 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Fri 17-07-20 00:12:15, Tetsuo Handa wrote:
> > syzbot is reporting that mmput() from shrinker function has a risk of
> > deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
> > kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
> > uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
> >
> > Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
> > callback") replaced mmput() with mmput_async() in order to avoid sleeping
> > with spinlock held. But this patch replaces mmput() with mmput_async() in
> > order not to start __mmput() from shrinker context.
> >
> > [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
> >
> > Reported-by: syzbot <syzbot+1068f09c44d151250c33@syzkaller.appspotmail.com>
> > Reported-by: syzbot <syzbot+e5344baa319c9a96edec@syzkaller.appspotmail.com>
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>
> Reviewed-by: Michal Hocko <mhocko@suse.com>

Acked-by: Todd Kjos <tkjos@google.com>

>
> Thanks!
>
> > ---
> >  drivers/android/binder_alloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> > index 42c672f1584e..cbe6aa77d50d 100644
> > --- a/drivers/android/binder_alloc.c
> > +++ b/drivers/android/binder_alloc.c
> > @@ -947,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> >               trace_binder_unmap_user_end(alloc, index);
> >       }
> >       mmap_read_unlock(mm);
> > -     mmput(mm);
> > +     mmput_async(mm);
> >
> >       trace_binder_unmap_kernel_start(alloc, index);
> >
> > --
> > 2.18.4
>
> --
> Michal Hocko
> SUSE Labs

Patch
diff mbox series

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 42c672f1584e..cbe6aa77d50d 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -947,7 +947,7 @@  enum lru_status binder_alloc_free_page(struct list_head *item,
 		trace_binder_unmap_user_end(alloc, index);
 	}
 	mmap_read_unlock(mm);
-	mmput(mm);
+	mmput_async(mm);
 
 	trace_binder_unmap_kernel_start(alloc, index);