linux-kernel - Re: [PATCH] exec: remove comparision of variable i_size of type loff_t against SIZE

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Message-ID: <20200227233935.GA176371@gmail.com>
Date:   Thu, 27 Feb 2020 15:39:35 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH] exec: remove comparision of variable i_size of type
 loff_t against SIZE_MAX

On Thu, Feb 27, 2020 at 03:31:33PM -0800, Scott Branden wrote:
> Remove comparision of (i_size > SIZE_MAX).
> i_size is of type loff_t and can not be great than SIZE_MAX (~(size_t)0).
> 
> Signed-off-by: Scott Branden <scott.branden@...adcom.com>
> ---
>  fs/exec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index db17be51b112..16c229752f74 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -919,7 +919,7 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
>  		ret = -EINVAL;
>  		goto out;
>  	}
> -	if (i_size > SIZE_MAX || (max_size > 0 && i_size > max_size)) {
> +	if (max_size > 0 && i_size > max_size) {
>  		ret = -EFBIG;
>  		goto out;
>  	}

Nope, loff_t is 64-bit while size_t can be 32-bit.  And this check is
intentional, see https://git.kernel.org/torvalds/c/691115c3513ec83e

- Eric