Great! We need to make sure this gets backported to 4.4 and 4.9, and to 
3.18 with the original dependency, please.

Thanks,

Paul

On 03/07/2018 01:48 PM, Nathan Chancellor wrote:
> On Wed, Mar 07, 2018 at 01:40:30PM -0800, Paul Lawrence wrote:
>> Regression introduced in commit ce8a3a9e76d0193e2e8d74a06d275b3c324ca652
>> ("staging: android: ashmem: Fix a race condition in pin ioctls")
>> causing deadlock.
>>
>> No need to hold ashmem_mutex while copying from user
>>
>> Stacks are:
>>
>> ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:379
>> mmap_region+0x7dd/0xfd0 mm/mmap.c:1694
>> do_mmap+0x57b/0xbe0 mm/mmap.c:1473
>>
>> and
>>
>> lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
>> __might_fault+0x14a/0x1d0 mm/memory.c:4014
>> copy_from_user arch/x86/include/asm/uaccess.h:705 [inline]
>> ashmem_pin_unpin drivers/staging/android/ashmem.c:719 [inline]
>>
>> Signed-off-by: Paul Lawrence <paullawrence@google.com>
>> Cc: <stable@vger.kernel.org> # 4.9.x
>> Cc: <stable@vger.kernel.org> # 4.4.x
>> Cc: <stable@vger.kernel.org> # 3.18.x: ce8a3a9e76d01
>> Cc: <stable@vger.kernel.org> # 3.18.x
>> Cc: Ben Hutchings <ben@decadent.org.uk>
>> ---
>>   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 6dbba5aff191..8c55706c2cfa 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;
>> -- 
>> 2.16.2.395.g2e18187dfd-goog
>>
> Hey Paul,
>
> Looks like this same patch is already in Greg's tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?id=740a5759bf222332fbb5eda42f89aa25ba38f9b2
>
> Cheers!
> Nathan Chancellor