4.9-stable review patch. If anyone has any objections, please let me know.
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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 @@ -718,16 +718,14 @@ 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;