On 2017年11月02日 20:56, Nikolay Borisov wrote:
>
>
> 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 <wqu@xxxxxxxx>
>>>> ---
>>>> 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_<something>_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_<something>_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!
Well, this makes sense.
I should merge them up.
Since verify_dir_item() just do extra check on types, they can be easily
merged.
The original plan is to have check_<some extra item> under
check_variable_length_item() if needed.
Considering only type and maximum name len need to be addded, it's quite
an easy work.
I'll add them in next update. (With extra possible checks).
Thanks,
Qu
>
>>
>> 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;
>>>> }
>>>>
>>> --
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>>>
>>
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