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 <[email protected]>
> ---
> 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
> + */
The comment is confusing (but so are the internals of accessing an
extent buffer and all the offset magic happening behind the scenes).
You are essentially opencoding btrfs_item_ptr_offset but instead of
pointing at the first entry in the data portion, you really point to
'cur' entry and in order to make it "accessor friendly" you do the +
BTRFS_LEAF_DATA_OFFSET. I'd say just put something like :
"This is the same as btrfs_item_ptr_offset but starting at item data
pointed by header_offset". In fact I'd suggest renaming header_offset to
data_offset
> + 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)
> +{
> + 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;
nit: Rename cur to cur_offset to make it clear this is an offset.
> +
> + 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;
> }
>
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