linux-kernel - Re: [PATCH 03/10] floppy: Fix MAX

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Message-ID: <9673d62f-e308-9c43-0318-e2f611f43eec@suse.cz>
Date:   Tue, 21 Mar 2023 08:53:13 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Denis Efremov <efremov@...ux.com>
Subject: Re: [PATCH 03/10] floppy: Fix MAX_ORDER usage

On 3/15/23 12:31, Kirill A. Shutemov wrote:
> MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
> can deliver is MAX_ORDER-1.
> 
> Fix MAX_ORDER usage in floppy code.
> 
> Also allocation buffer exactly PAGE_SIZE << MAX_ORDER bytes is okay. Fix
> MAX_LEN check.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> Cc: Denis Efremov <efremov@...ux.com>
> ---
>  drivers/block/floppy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index 487840e3564d..90d2dfb6448e 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3079,7 +3079,7 @@ static void raw_cmd_free(struct floppy_raw_cmd **ptr)
>  	}
>  }
>  
> -#define MAX_LEN (1UL << MAX_ORDER << PAGE_SHIFT)
> +#define MAX_LEN (1UL << (MAX_ORDER - 1) << PAGE_SHIFT)
>  
>  static int raw_cmd_copyin(int cmd, void __user *param,
>  				 struct floppy_raw_cmd **rcmd)
> @@ -3108,7 +3108,7 @@ static int raw_cmd_copyin(int cmd, void __user *param,
>  	ptr->resultcode = 0;
>  
>  	if (ptr->flags & (FD_RAW_READ | FD_RAW_WRITE)) {
> -		if (ptr->length <= 0 || ptr->length >= MAX_LEN)
> +		if (ptr->length <= 0 || ptr->length > MAX_LEN)
>  			return -EINVAL;
>  		ptr->kernel_data = (char *)fd_dma_mem_alloc(ptr->length);
>  		fallback_on_nodma_alloc(&ptr->kernel_data, ptr->length);