Re: usb: f_fs: Fix CFI failure in ki_complete

[Prashanth K <quic_prashk@quicinc.com>]

On 12-12-22 07:05 pm, Greg Kroah-Hartman wrote:
> On Mon, Dec 12, 2022 at 06:54:24PM +0530, Prashanth K wrote:
>> Function pointer ki_complete() expects 'long' as its second
>> argument, but we pass integer from ffs_user_copy_worker. This
>> might cause a CFI failure, as ki_complete is an indirect call
>> with mismatched prototype. Fix this by typecasting the second
>> argument to long.
> 
> "might"?  Does it or not?  If it does, why hasn't this been reported
> before?
Sorry for the confusion in commit text, We caught a CFI (Control Flow 
Integrity) failure internally on 5.15, hence pushed this patch. But 
later I came to know that CFI was implemented on 5.4 kernel for Android. 
Will push the same on ACK and share the related details there.

Thanks.
> 
>> Cc: <stable@vger.kernel.org> # 5.15
> 
> CFI first showed up in 6.1, not 5.15, right?
> 
>> Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
>>
>> ---
>>   drivers/usb/gadget/function/f_fs.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
>> index 73dc10a7..9c26561 100644
>> --- a/drivers/usb/gadget/function/f_fs.c
>> +++ b/drivers/usb/gadget/function/f_fs.c
>> @@ -835,7 +835,7 @@ static void ffs_user_copy_worker(struct work_struct *work)
>>   		kthread_unuse_mm(io_data->mm);
>>   	}
>>   
>> -	io_data->kiocb->ki_complete(io_data->kiocb, ret);
>> +	io_data->kiocb->ki_complete(io_data->kiocb, (long)ret);
> 
> Why just fix up this one instance?  What about ep_user_copy_worker()?
> And what about all other calls to ki_complete that are not using a
> (long) cast?
> 
> This feels wrong, what exactly is the reported error and how come other
> kernel calls to this function pointer have not had a problem with CFI?
> ceph_aio_complete() would be another example, right?
> 
> thanks,
> 
> greg k-h