From 95b1d336b0642198b56836b89908d07b9a0c9608 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Fri, 1 Dec 2023 17:21:32 +0000 Subject: binder: fix race between mmput() and do_exit() commit 9a9ab0d963621d9d12199df9817e66982582d5a5 upstream. Task A calls binder_update_page_range() to allocate and insert pages on a remote address space from Task B. For this, Task A pins the remote mm via mmget_not_zero() first. This can race with Task B do_exit() and the final mmput() refcount decrement will come from Task A. Task A | Task B ------------------+------------------ mmget_not_zero() | | do_exit() | exit_mm() | mmput() mmput() | exit_mmap() | remove_vma() | fput() | In this case, the work of ____fput() from Task B is queued up in Task A as TWA_RESUME. So in theory, Task A returns to userspace and the cleanup work gets executed. However, Task A instead sleep, waiting for a reply from Task B that never comes (it's dead). This means the binder_deferred_release() is blocked until an unrelated binder event forces Task A to go back to userspace. All the associated death notifications will also be delayed until then. In order to fix this use mmput_async() that will schedule the work in the corresponding mm->async_put_work WQ instead of Task A. Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Reviewed-by: Alice Ryhl Signed-off-by: Carlos Llamas Link: https://lore.kernel.org/r/20231201172212.1813387-4-cmllamas@google.com [cmllamas: fix trivial conflict with missing d8ed45c5dcd4.] Signed-off-by: Carlos Llamas Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index c90a324e0e87..327e19bb807f 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -290,7 +290,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, } if (mm) { up_read(&mm->mmap_sem); - mmput(mm); + mmput_async(mm); } return 0; @@ -325,7 +325,7 @@ err_page_ptr_cleared: err_no_vma: if (mm) { up_read(&mm->mmap_sem); - mmput(mm); + mmput_async(mm); } return vma ? -ENOMEM : -ESRCH; } -- cgit v1.2.3