linux-ext4 - Re: [PATCH 2/2] ext4: remove ext4_xattr_check

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Date:   Tue, 21 Mar 2017 16:31:58 +0100
From:   Jan Kara <jack@...e.cz>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH 2/2] ext4: remove ext4_xattr_check_entry()

On Tue 14-03-17 21:50:56, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> ext4_xattr_check_entry() was redundant with validation of the full xattr
> entries list in ext4_xattr_check_entries(), which all callers also did.
> ext4_xattr_check_entry() also didn't actually do correct validation;
> specifically, it never checked that the value doesn't overlap the xattr
> names, nor did it account for padding when checking whether the xattr
> value overflows the available space.  So remove it to eliminate any
> potential confusion.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

So there's a slight difference that ext4_xattr_check_names() gets called
only when loading block on disk so it does not discover corruption in
memory which this check had a potential to check. But I guess there's no
big point in these checks so:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/xattr.c | 30 ++++++------------------------
>  1 file changed, 6 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 71bf40933bbb..b4364612a66f 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -249,20 +249,9 @@ __xattr_check_inode(struct inode *inode, struct ext4_xattr_ibody_header *header,
>  #define xattr_check_inode(inode, header, end) \
>  	__xattr_check_inode((inode), (header), (end), __func__, __LINE__)
>  
> -static inline int
> -ext4_xattr_check_entry(struct ext4_xattr_entry *entry, size_t size)
> -{
> -	size_t value_size = le32_to_cpu(entry->e_value_size);
> -
> -	if (entry->e_value_block != 0 || value_size > size ||
> -	    le16_to_cpu(entry->e_value_offs) + value_size > size)
> -		return -EFSCORRUPTED;
> -	return 0;
> -}
> -
>  static int
>  ext4_xattr_find_entry(struct ext4_xattr_entry **pentry, int name_index,
> -		      const char *name, size_t size, int sorted)
> +		      const char *name, int sorted)
>  {
>  	struct ext4_xattr_entry *entry;
>  	size_t name_len;
> @@ -282,8 +271,6 @@ ext4_xattr_find_entry(struct ext4_xattr_entry **pentry, int name_index,
>  			break;
>  	}
>  	*pentry = entry;
> -	if (!cmp && ext4_xattr_check_entry(entry, size))
> -		return -EFSCORRUPTED;
>  	return cmp ? -ENODATA : 0;
>  }
>  
> @@ -311,7 +298,6 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
>  	ea_bdebug(bh, "b_count=%d, refcount=%d",
>  		atomic_read(&(bh->b_count)), le32_to_cpu(BHDR(bh)->h_refcount));
>  	if (ext4_xattr_check_block(inode, bh)) {
> -bad_block:
>  		EXT4_ERROR_INODE(inode, "bad block %llu",
>  				 EXT4_I(inode)->i_file_acl);
>  		error = -EFSCORRUPTED;
> @@ -319,9 +305,7 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
>  	}
>  	ext4_xattr_cache_insert(ext4_mb_cache, bh);
>  	entry = BFIRST(bh);
> -	error = ext4_xattr_find_entry(&entry, name_index, name, bh->b_size, 1);
> -	if (error == -EFSCORRUPTED)
> -		goto bad_block;
> +	error = ext4_xattr_find_entry(&entry, name_index, name, 1);
>  	if (error)
>  		goto cleanup;
>  	size = le32_to_cpu(entry->e_value_size);
> @@ -358,13 +342,12 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
>  		return error;
>  	raw_inode = ext4_raw_inode(&iloc);
>  	header = IHDR(inode, raw_inode);
> -	entry = IFIRST(header);
>  	end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
>  	error = xattr_check_inode(inode, header, end);
>  	if (error)
>  		goto cleanup;
> -	error = ext4_xattr_find_entry(&entry, name_index, name,
> -				      end - (void *)entry, 0);
> +	entry = IFIRST(header);
> +	error = ext4_xattr_find_entry(&entry, name_index, name, 0);
>  	if (error)
>  		goto cleanup;
>  	size = le32_to_cpu(entry->e_value_size);
> @@ -799,7 +782,7 @@ ext4_xattr_block_find(struct inode *inode, struct ext4_xattr_info *i,
>  		bs->s.end = bs->bh->b_data + bs->bh->b_size;
>  		bs->s.here = bs->s.first;
>  		error = ext4_xattr_find_entry(&bs->s.here, i->name_index,
> -					      i->name, bs->bh->b_size, 1);
> +					      i->name, 1);
>  		if (error && error != -ENODATA)
>  			goto cleanup;
>  		bs->s.not_found = error;
> @@ -1068,8 +1051,7 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i,
>  			return error;
>  		/* Find the named attribute. */
>  		error = ext4_xattr_find_entry(&is->s.here, i->name_index,
> -					      i->name, is->s.end -
> -					      (void *)is->s.base, 0);
> +					      i->name, 0);
>  		if (error && error != -ENODATA)
>  			return error;
>  		is->s.not_found = error;
> -- 
> 2.12.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR