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Message-ID: <20231102185934.773885-4-cmllamas@google.com>
Date: Thu, 2 Nov 2023 18:59:04 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Arve Hjønnevåg" <arve@...roid.com>,
Todd Kjos <tkjos@...roid.com>,
Martijn Coenen <maco@...roid.com>,
Joel Fernandes <joel@...lfernandes.org>,
Christian Brauner <brauner@...nel.org>,
Carlos Llamas <cmllamas@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Brian Swetland <swetland@...gle.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 03/21] binder: fix race between mmput() and do_exit()
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")
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
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 c4d60d81221b..046c3ae9eb8f 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -271,7 +271,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
}
if (mm) {
mmap_write_unlock(mm);
- mmput(mm);
+ mmput_async(mm);
}
return 0;
@@ -304,7 +304,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
err_no_vma:
if (mm) {
mmap_write_unlock(mm);
- mmput(mm);
+ mmput_async(mm);
}
return vma ? -ENOMEM : -ESRCH;
}
--
2.42.0.869.gea05f2083d-goog
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