Messages in this thread | | | Subject | Re: [Linaro-mm-sig] [PATCHv3 2/2] staging: android: ion: Add ioctl to query available heaps | From | Laura Abbott <> | Date | Wed, 7 Sep 2016 17:14:48 -0700 |
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On 09/07/2016 12:37 PM, Arnd Bergmann wrote: > On Wednesday, September 7, 2016 11:49:59 AM CEST Laura Abbott wrote: > >> - if (dir & _IOC_WRITE) >> - if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd))) >> - return -EFAULT; >> + /* >> + * The copy_from_user is unconditional here for both read and write >> + * to do the validate. If there is no write for the ioctl, the >> + * buffer is cleared >> + */ >> + if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd))) >> + return -EFAULT; >> + >> + ret = validate_ioctl_arg(cmd, &data); >> + if (WARN_ON_ONCE(ret)) >> + return ret; > > I noticed that the WARN_ON_ONCE warns about invalid user input, > but I think we tend to normally just use WARN_ON for things that > go wrong inside of the kernel or in hardware. > > Maybe better use printk_once() or printk_ratelimited. >
Sure, the error code should hopefully be enough of a hint to userspace to maybe check the log.
> Is there any noticeable overhead in always copying the structure? > copy_from_user() can be a bit slow depending on debugging or > security features, and it seems unnecessary if the validation > is only done for one of the commands. >
Good point. It made sense with some of the other ioctls (specifically the ABI) but isn't necessary now. We can evaluate later when other ioctls get added.
> Otherwise the patch looks good to me. > > Arnd >
Thanks!
Laura
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