linux-kernel - Re: Bad ext3/nfs DoS bug

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Message-ID: <20060721142415.GC2020@atrey.karlin.mff.cuni.cz>
Date:	Fri, 21 Jul 2006 16:24:15 +0200
From:	Jan Kara <jack@...e.cz>
To:	Neil Brown <neilb@...e.de>
Cc:	James <20@...ingley.org>, Marcel Holtmann <marcel@...tmann.org>,
	linux-kernel@...r.kernel.org, akpm@...l.org, sct@...hat.com
Subject: Re: Bad ext3/nfs DoS bug

> On Thursday July 20, jack@...e.cz wrote:
> >   Yes, that looks fine too. I did not realize that we get the inode
> > number only in a few places. Maybe we could wrap the checks in a
> > function (possibly inline) so that the checks are just in one place?
> 
> Like this?
  Yes.

> NeilBrown
> 
> 
> Avoid triggering ext3_error on bad NFS file handle
> 
> The inode number out of an NFS file handle gets passed 
> eventually to ext3_get_inode_block without any checking.
> If ext3_get_inode_block allows it to trigger a error,
> then bad filehandles can have unpleasant effect.
> 
> So remove the call to ext3_error there and put a matching
> check in ext3/namei.c where inode numbers are read of storage.
> 
> Signed-off-by: Neil Brown <neilb@...e.de>
  Signed-off-by: Jan Kara <jack@...e.cz>

							Honza

> ### Diffstat output
>  ./fs/ext3/inode.c         |   13 ++++++-------
>  ./fs/ext3/namei.c         |   15 +++++++++++++--
>  ./include/linux/ext3_fs.h |    9 +++++++++
>  3 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff .prev/fs/ext3/inode.c ./fs/ext3/inode.c
> --- .prev/fs/ext3/inode.c	2006-07-20 14:41:07.000000000 +1000
> +++ ./fs/ext3/inode.c	2006-07-21 16:36:32.000000000 +1000
> @@ -2402,14 +2402,13 @@ static ext3_fsblk_t ext3_get_inode_block
>  	struct buffer_head *bh;
>  	struct ext3_group_desc * gdp;
>  
> -
> -	if ((ino != EXT3_ROOT_INO && ino != EXT3_JOURNAL_INO &&
> -		ino != EXT3_RESIZE_INO && ino < EXT3_FIRST_INO(sb)) ||
> -		ino > le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count)) {
> -		ext3_error(sb, "ext3_get_inode_block",
> -			    "bad inode number: %lu", ino);
> +	if (!ext3_valid_inum(sb, ino))
> +		/* This error already checked for in namei.c unless we
> +		 * are looking at an NFS filehandle, in which case,
> +		 * no error reported is needed
> +		 */
>  		return 0;
> -	}
> +
>  	block_group = (ino - 1) / EXT3_INODES_PER_GROUP(sb);
>  	if (block_group >= EXT3_SB(sb)->s_groups_count) {
>  		ext3_error(sb,"ext3_get_inode_block","group >= groups count");
> 
> diff .prev/fs/ext3/namei.c ./fs/ext3/namei.c
> --- .prev/fs/ext3/namei.c	2006-07-20 14:39:51.000000000 +1000
> +++ ./fs/ext3/namei.c	2006-07-21 16:36:09.000000000 +1000
> @@ -1000,7 +1000,12 @@ static struct dentry *ext3_lookup(struct
>  	if (bh) {
>  		unsigned long ino = le32_to_cpu(de->inode);
>  		brelse (bh);
> -		inode = iget(dir->i_sb, ino);
> +		if (!ext3_valid_inum(dir->i_sb, ino)) {
> +			ext3_error(dir->i_sb, "ext3_lookup",
> +				   "bad inode number: %lu", ino);
> +			inode = NULL;
> +		} else
> +			inode = iget(dir->i_sb, ino);
>  
>  		if (!inode)
>  			return ERR_PTR(-EACCES);
> @@ -1028,7 +1033,13 @@ struct dentry *ext3_get_parent(struct de
>  		return ERR_PTR(-ENOENT);
>  	ino = le32_to_cpu(de->inode);
>  	brelse(bh);
> -	inode = iget(child->d_inode->i_sb, ino);
> +
> +	if (!ext3_valid_inum(child->d_inode->i_sb, ino)) {
> +		ext3_error(child->d_inode->i_sb, "ext3_get_parent",
> +			   "bad inode number: %lu", ino);
> +		inode = NULL;
> +	} else
> +		inode = iget(child->d_inode->i_sb, ino);
>  
>  	if (!inode)
>  		return ERR_PTR(-EACCES);
> 
> diff .prev/include/linux/ext3_fs.h ./include/linux/ext3_fs.h
> --- .prev/include/linux/ext3_fs.h	2006-07-21 16:34:01.000000000 +1000
> +++ ./include/linux/ext3_fs.h	2006-07-21 16:35:55.000000000 +1000
> @@ -492,6 +492,15 @@ static inline struct ext3_inode_info *EX
>  {
>  	return container_of(inode, struct ext3_inode_info, vfs_inode);
>  }
> +
> +static inline int ext3_valid_inum(struct super_block *sb, unsigned long ino)
> +{
> +	return ino == EXT3_ROOT_INO ||
> +		ino == EXT3_JOURNAL_INO ||
> +		ino == EXT3_RESIZE_INO ||
> +		(ino > EXT3_FIRST_INO(sb) &&
> +		 ino <= le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count));
> +}
>  #else
>  /* Assume that user mode programs are passing in an ext3fs superblock, not
>   * a kernel struct super_block.  This will allow us to call the feature-test
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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