RE: [PATCH V5 3/4] Move stack parameters for sed_ioctl to prevent oversized stack with CONFIG_KASAN

[David Laight]

From: Scott Bauer Sent: 13 February 2017 16:11
> When CONFIG_KASAN is enabled, compilation fails:
> 
> block/sed-opal.c: In function 'sed_ioctl':
> block/sed-opal.c:2447:1: error: the frame size of 2256 bytes is larger than 2048 bytes [-Werror=frame-
> larger-than=]
> 
> Moved all the ioctl structures off the stack and dynamically activate
> using _IOC_SIZE()

Think I'd not that this simplifies the code considerably.
AFAICT CONFIG_KASAN is a just brainf*ck.
It at least needs annotation that copy_from_user() has properties
similar to memset().
So if the size matches that of the type then no guard space (etc)
is required.

...
> +	ioctl_ptr = memdup_user(arg,  _IOC_SIZE(cmd));
> +	if (IS_ERR_OR_NULL(ioctl_ptr)) {
> +		ret = PTR_ERR(ioctl_ptr);
> +		goto out;
...
> + out:
> +	kfree(ioctl_ptr);
> +	return ret;
>  }

That error path doesn't look quite right to me.

	David