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+d7a918a7a8e1c952b...@syzkaller.appspotmail.com Signed-off-by: Yisheng Xie <xieyishe...@huawei.com> --- drivers/staging/android/ashmem.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index 6dbba5a..8c55706 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -702,16 +702,14 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd, 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; -- 1.7.12.4 _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel