linux-kernel - Re: [patch 2/2] misc: mic/scif: fix wrap around tests

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Date:	Sun, 11 Oct 2015 02:14:44 -0700
From:	Sudeep Dutt <sudeep.dutt@...el.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Sudeep Dutt <sudeep.dutt@...el.com>,
	Nikhil Rao <nikhil.rao@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch 2/2] misc: mic/scif: fix wrap around tests

On Fri, 2015-10-09 at 09:40 +0300, Dan Carpenter wrote:
> Signed integer overflow is undefined.  Also I added a check for
> "(offset < 0)" in scif_unregister() because that makes it match the
> other conditions and because I didn't want to subtract a negative.
> 
> Fixes: ba612aa8b487 ('misc: mic: SCIF memory registration and unregistration')
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> 
> Imagine you are on 64 bit and len is larger than INT_MAX << 12, it means
> that we truncate it because scif_get_window_offset() takes an integer
> argument.  I don't know if this is an issue. 

scif_get_window_offset(..) takes an integer argument for the number of
pages. We believe that an int for number of 4K pages is sufficient for
current systems. I don't think there is an issue here.

>  Maybe I should use
> INT_MAX instead of LONG_MAX?  I am working on a static checker warning
> for these types of issues:
> drivers/misc/mic/scif/scif_rma.c:1631 scif_register() warn: truncating user data 'len >> 12' '0-4503599627370495'
> drivers/misc/mic/scif/scif_rma.c:1643 scif_register() warn: truncating user data 'len >> 12' '0-4503599627370495'
> 
> The other static warnings here are:
> 
> drivers/misc/mic/scif/scif_rma.c:745 scif_unregister_window() warn: inconsistent returns 'mutex:&ep->rma_info.rma_lock'.
>   Locked on:   line 745
>   Unlocked on: line 687

The function expects the lock to be held by the caller so there is no
issue here.

> drivers/misc/mic/scif/scif_rma.c:1463 scif_unpin_pages() warn: passing __func__ while the format string already contains the name of the function 'scif_unpin_pages'
> 

It might be useful to enhance checkpatch to catch such issues.

> diff --git a/drivers/misc/mic/scif/scif_rma.c b/drivers/misc/mic/scif/scif_rma.c
> index bc2dccb..fea7d2c 100644
> --- a/drivers/misc/mic/scif/scif_rma.c
> +++ b/drivers/misc/mic/scif/scif_rma.c
> @@ -1510,7 +1510,7 @@ off_t scif_register_pinned_pages(scif_epd_t epd,
>  	if ((map_flags & SCIF_MAP_FIXED) &&
>  	    ((ALIGN(offset, PAGE_SIZE) != offset) ||
>  	    (offset < 0) ||
> -	    (offset + (off_t)len < offset)))
> +	    (len > LONG_MAX - offset)))
>  		return -EINVAL;
>  
>  	might_sleep();
> @@ -1613,7 +1613,7 @@ off_t scif_register(scif_epd_t epd, void *addr, size_t len, off_t offset,
>  	if ((map_flags & SCIF_MAP_FIXED) &&
>  	    ((ALIGN(offset, PAGE_SIZE) != offset) ||
>  	    (offset < 0) ||
> -	    (offset + (off_t)len < offset)))
> +	    (len < LONG_MAX - offset)))

Why is this change required? The earlier code was being used to detect
wraparound and I think it works fine.

Thanks,
Sudeep Dutt

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