This is a note to let you know that I've just added the patch titled

staging: android: ashmem: Fix possible deadlock in ashmem_ioctl

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: staging-android-ashmem-fix-possible-deadlock-in-ashmem_ioctl.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 740a5759bf222332fbb5eda42f89aa25ba38f9b2 Mon Sep 17 00:00:00 2001

From: Yisheng Xie xieyisheng1@huawei.com Date: Wed, 28 Feb 2018 14:59:22 +0800 Subject: staging: android: ashmem: Fix possible deadlock in ashmem_ioctl

From: Yisheng Xie xieyisheng1@huawei.com

commit 740a5759bf222332fbb5eda42f89aa25ba38f9b2 upstream.

ashmem_mutex may create a chain of dependencies like:

CPU0 CPU1 mmap syscall ioctl syscall -> mmap_sem (acquired) -> ashmem_ioctl -> ashmem_mmap -> ashmem_mutex (acquired) -> ashmem_mutex (try to acquire) -> copy_from_user -> mmap_sem (try to acquire)

There is a lock odering problem between mmap_sem and ashmem_mutex causing a lockdep splat[1] during a syzcaller test. This patch fixes the problem by move copy_from_user out of ashmem_mutex.

[1] https://www.spinics.net/lists/kernel/msg2733200.html

Fixes: ce8a3a9e76d0 (staging: android: ashmem: Fix a race condition in pin ioctls) Reported-by: syzbot+d7a918a7a8e1c952bc36@syzkaller.appspotmail.com Signed-off-by: Yisheng Xie xieyisheng1@huawei.com Cc: "Joel Fernandes (Google)" joel.opensrc@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- drivers/staging/android/ashmem.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -709,16 +709,14 @@ static int ashmem_pin_unpin(struct ashme size_t pgstart, pgend; int ret = -EINVAL;

+ if (unlikely(copy_from_user(&pin, p, sizeof(pin)))) + return -EFAULT; + mutex_lock(&ashmem_mutex);

if (unlikely(!asma->file)) goto out_unlock;

- if (unlikely(copy_from_user(&pin, p, sizeof(pin)))) { - ret = -EFAULT; - goto out_unlock; - } - /* per custom, you can pass zero for len to mean "everything onward" */ if (!pin.len) pin.len = PAGE_ALIGN(asma->size) - pin.offset;

Patches currently in stable-queue which might be from xieyisheng1@huawei.com are

queue-4.15/staging-android-ashmem-fix-possible-deadlock-in-ashmem_ioctl.patch