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staging: android: ashmem: Fix possible deadlock in ashmem_ioctl

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yisheng Xie 2018-02-28 14:59:22 +08:00 committed by Greg Kroah-Hartman
parent a42ae59051
commit 740a5759bf
1 changed files with 3 additions and 5 deletions
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8
drivers/staging/android/ashmem.c
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@ -701,16 +701,14 @@ 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;