On 2017年11月02日 20:06, 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 <[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).
The sentence inside the brackets is the point. :)
>
> 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
Only if we can ensure all offsets passed in are starting after header,
then I'm OK to rename it to "data_offset"
The "header_offset" here is to info any caller that one should pass
"normal" offset here, to avoid possible LEAF_DATA_OFFSET hassle.
Thanks,
Qu
>
>> + 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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