From: Andreas Dilger <adilger@sun.com>
Subject: Re: [PATCH] ext4: fix online resize group descriptors corruption
Date: Thu, 12 Jun 2008 04:59:45 -0600
Message-ID: <20080612105945.GB3726@webber.adilger.int>
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Cc: tytso@mit.edu, linux-ext4@vger.kernel.org
To: =?utf-8?Q?Fr=E9d=E9ric_Boh=E9?= <frederic.bohe@bull.net>
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On Jun 12, 2008  11:42 +0200, Fr=EF=BF=BDd=EF=BF=BDric Boh=EF=BF=BD wro=
te:
> From: Frederic Bohe <frederic.bohe@bull.net>
>=20
> This is the patch for the group descriptor table corruption during
> online resize pointed out by Theodore Tso.
> The issue was due to the ext4 group descriptor which can be either
> 32 or 64 bytes long.
> Only the 64 bytes structure was taken into account.
>=20
> diff -rup a/fs/ext4/resize.c b/fs/ext4/resize.c
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -855,7 +855,8 @@ int ext4_group_add(struct super_block *s
>  	 */
> =20
>  	/* Update group descriptor block for new group */
> -	gdp =3D (struct ext4_group_desc *)primary->b_data + gdb_off;
> +	gdp =3D (struct ext4_group_desc *)(
> +	       (__u8 *)primary->b_data + gdb_off * EXT4_DESC_SIZE(sb));

Normally pointer arithmetic is done by casting to (char *)...
Otherwise, patch looks sensible, though it could be reformatted to=20
match the normal coding style a bit better:

	gdp =3D (struct ext4_group_desc *)((char *)primary->b_data +
					 gdb_off * EXT4_DESC_SIZE(sb));

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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