linux-kernel - Re: [PATCH linux-next] befs: befs_fill

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Date:	Tue, 12 Feb 2013 09:46:19 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tim Gardner <tim.gardner@...onical.com>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH linux-next] befs: befs_fill_super(): remove unreachable code

Tim Gardner <tim.gardner@...onical.com> writes:

> befs_sb->num_blocks is of base type u64 which is the same as sector_t.
> Therefore, num_blocks can never be larger then the maximum
> value of sector_t.

The analysys is wrong.  On 32bit with CONFIG_LBAF unset sector_t is an
unsigned long aka a u32, while befs_off_t is always a u64.

Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

> smatch analysis:
>
> fs/befs/linuxvfs.c:851 befs_fill_super() warn: impossible
>  condition '(befs_sb->num_blocks > ~(0)) => (0-u64max > u64max)'
>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> ---
>  fs/befs/linuxvfs.c |    7 -------
>  1 file changed, 7 deletions(-)
>
> diff --git a/fs/befs/linuxvfs.c b/fs/befs/linuxvfs.c
> index 2b3bda8..2ce5705 100644
> --- a/fs/befs/linuxvfs.c
> +++ b/fs/befs/linuxvfs.c
> @@ -848,13 +848,6 @@ befs_fill_super(struct super_block *sb, void *data, int silent)
>  	if (befs_check_sb(sb) != BEFS_OK)
>  		goto unacquire_priv_sbp;
>  
> -	if( befs_sb->num_blocks > ~((sector_t)0) ) {
> -		befs_error(sb, "blocks count: %Lu "
> -			"is larger than the host can use",
> -			befs_sb->num_blocks);
> -		goto unacquire_priv_sbp;
> -	}
> -
>  	/*
>  	 * set up enough so that it can read an inode
>  	 * Fill in kernel superblock fields from private sb
--
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