From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:50556 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754988AbdKBM4E (ORCPT ); Thu, 2 Nov 2017 08:56:04 -0400 Subject: Re: [PATCH 1/2] btrfs: tree-checker: Add checker for variable length item To: Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org Cc: dsterba@suse.cz References: <20171101121450.6297-1-wqu@suse.com> From: Nikolay Borisov Message-ID: <0a79c9cd-ba67-293a-2981-3182775eda90@suse.com> Date: Thu, 2 Nov 2017 14:56:01 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2.11.2017 14:48, Qu Wenruo wrote: > > > On 2017年11月02日 20:12, Nikolay Borisov wrote: >> >> >> On 1.11.2017 14:14, Qu Wenruo wrote: >>> For the following types, we have items with variable length: >>> (With BTRFS_ prefix and _KEY suffix snipped) >>> >>> DIR_ITEM >>> DIR_INDEX >>> XATTR_ITEM >>> INODE_REF >>> INODE_EXTREF >>> ROOT_REF >>> ROOT_BACKREF >>> >>> They all use @name_len to indicate their name length, and XATTR_ITEM has >>> extra @data_len to indicate it data length. >>> >>> Despite their variable length, it's also possible to have several such >>> structure inside one item. >>> >>> This patch will add checker to ensure: >>> >>> 1) No structure header and its data cross item boundary >>> 2) Except XATTR_ITEM, no structure should have non-zero @data_len >>> >>> This checker is especially useful to avoid possible access beyond >>> boundary for fuzzed image. >>> >>> Signed-off-by: Qu Wenruo >>> --- >>> fs/btrfs/tree-checker.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 123 insertions(+) >>> >>> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c >>> index 114fc5f0ecc5..f26e86fcbd74 100644 >>> --- a/fs/btrfs/tree-checker.c >>> +++ b/fs/btrfs/tree-checker.c >>> @@ -222,6 +222,120 @@ static int check_csum_item(struct btrfs_root *root, struct extent_buffer *leaf, >>> return 0; >>> } >>> >>> +static u32 get_header_size(u8 type) >>> +{ >>> + switch (type) { >>> + case BTRFS_DIR_ITEM_KEY: >>> + case BTRFS_DIR_INDEX_KEY: >>> + case BTRFS_XATTR_ITEM_KEY: >>> + return sizeof(struct btrfs_dir_item); >>> + case BTRFS_INODE_REF_KEY: >>> + return sizeof(struct btrfs_inode_ref); >>> + case BTRFS_INODE_EXTREF_KEY: >>> + return sizeof(struct btrfs_inode_extref); >>> + case BTRFS_ROOT_REF_KEY: >>> + case BTRFS_ROOT_BACKREF_KEY: >>> + return sizeof(struct btrfs_root_ref); >>> + } >>> + WARN_ON(1); >>> + return 0; >>> +} >>> + >>> +static u16 get_header_namelen(struct extent_buffer *leaf, u8 type, >>> + u32 header_offset) >>> +{ >>> + /* >>> + * @header_offset is offset starts after leaf header, while the >>> + * accessors expects offset starts from leaf header. >>> + * Sowe need to adds LEAF_DATA_OFFSET here >>> + */ >>> + unsigned long leaf_offset = header_offset + BTRFS_LEAF_DATA_OFFSET; >>> + >>> + switch (type) { >>> + case BTRFS_DIR_ITEM_KEY: >>> + case BTRFS_DIR_INDEX_KEY: >>> + case BTRFS_XATTR_ITEM_KEY: >>> + return btrfs_dir_name_len(leaf, (void *)leaf_offset); >>> + case BTRFS_INODE_REF_KEY: >>> + return btrfs_inode_ref_name_len(leaf, (void *)leaf_offset); >>> + case BTRFS_INODE_EXTREF_KEY: >>> + return btrfs_inode_extref_name_len(leaf, (void *)leaf_offset); >>> + case BTRFS_ROOT_REF_KEY: >>> + case BTRFS_ROOT_BACKREF_KEY: >>> + return btrfs_root_ref_name_len(leaf, (void *)leaf_offset); >>> + } >>> + WARN_ON(1); >>> + return 0; >>> +} >>> + >>> +static u16 get_header_datalen(struct extent_buffer *leaf, u8 type, >>> + unsigned long header_offset) >>> +{ >>> + /* Same as get_header_namelen */ >>> + unsigned long leaf_offset = header_offset + BTRFS_LEAF_DATA_OFFSET; >>> + >>> + switch (type) { >>> + case BTRFS_DIR_ITEM_KEY: >>> + case BTRFS_DIR_INDEX_KEY: >>> + case BTRFS_XATTR_ITEM_KEY: >>> + return btrfs_dir_data_len(leaf, (void *)leaf_offset); >>> + } >>> + return 0; >>> +} >>> + >>> +/* >>> + * For items with variable length, normally with namelen and tailing data. >>> + * Like INODE_REF or XATTR >>> + */ >>> +static int check_variable_length_item(struct btrfs_root *root, >>> + struct extent_buffer *leaf, >>> + struct btrfs_key *key, int slot) >>> +{ >> >> One more thing - you are only validating the boundaries of such variable >> length items, so make this specific. I.e rename the function to >> something like: > > If you follow the naming schema in tree-checker, you'll find that we (at > least myself) is naming these function always using "check_" prefix, so > "validate_" prefix seems less consistent. > > Further more, the naming has its level" > leaf (all items boundary already checked) > |- leaf_item (hub wrapper) > |- csum_item > |- extent_data_item > > So here check__item follows the original level according to > the naming schema. > > Further more, although we're checking boundary, the truth is, we are > check the name_len/data_len *members*, so the check__item > still makes sence. > > If really want to change the name, I prefer some naming can show that > we're checking several items which share the same variable length property. > > So at least, none of the alternative seems to fit the schema. The reason why I wanted this function renamed is that we have this function which performs only some checks and then we have the verify_dir_item which performs different checks for the same item. So why can't those function be turned into one ? I'm not too hung up on the actual naming! > > Thanks, > Qu > >> >> validate_variable_boundaries >> check_variable_length_item_boundary >> check_item_boundaries >> >>> + u8 type = key->type; >>> + u32 item_start = btrfs_item_offset_nr(leaf, slot); >>> + u32 item_end = btrfs_item_end_nr(leaf, slot); >>> + u32 header_size = get_header_size(type); >>> + u32 total_size; >>> + u32 cur = item_start; >>> + >>> + while (cur < item_end) { >>> + u32 namelen; >>> + u32 datalen; >>> + >>> + /* header itself should not cross item boundary */ >>> + if (cur + header_size > item_end) { >>> + generic_err(root, leaf, slot, >>> + "structure header crosses item boundary, have %u expect (%u, %u]", >>> + cur + header_size, cur, item_end); >>> + return -EUCLEAN; >>> + } >>> + >>> + namelen = get_header_namelen(leaf, type, cur); >>> + datalen = get_header_datalen(leaf, type, cur); >>> + >>> + /* Only XATTR can own data */ >>> + if (type != BTRFS_XATTR_ITEM_KEY && datalen) { >>> + generic_err(root, leaf, slot, >>> + "item has invalid data len, have %u expect 0", >>> + datalen); >>> + return -EUCLEAN; >>> + } >>> + >>> + total_size = header_size + namelen + datalen; >>> + >>> + /* header and name/data should not cross item boundary */ >>> + if (cur + total_size > item_end) { >>> + generic_err(root, leaf, slot, >>> + "structure data crosses item boundary, have %u expect (%u, %u]", >>> + cur + total_size, cur + header_size, item_end); >>> + return -EUCLEAN; >>> + } >>> + >>> + cur += total_size; >>> + } >>> + return 0; >>> +} >>> + >>> /* >>> * Common point to switch the item-specific validation. >>> */ >>> @@ -238,6 +352,15 @@ static int check_leaf_item(struct btrfs_root *root, >>> case BTRFS_EXTENT_CSUM_KEY: >>> ret = check_csum_item(root, leaf, key, slot); >>> break; >>> + case BTRFS_DIR_ITEM_KEY: >>> + case BTRFS_XATTR_ITEM_KEY: >>> + case BTRFS_DIR_INDEX_KEY: >>> + case BTRFS_INODE_REF_KEY: >>> + case BTRFS_INODE_EXTREF_KEY: >>> + case BTRFS_ROOT_REF_KEY: >>> + case BTRFS_ROOT_BACKREF_KEY: >>> + ret = check_variable_length_item(root, leaf, key, slot); >>> + break; >>> } >>> return ret; >>> } >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >