On 2019/3/12 下午4:28, Nikolay Borisov wrote:
>
>
> On 12.03.19 г. 9:45 ч., Qu Wenruo wrote:
>> [BUG]
>> When reading a file from a fuzzed image, kernel can panic like:
>> BTRFS warning (device loop0): csum failed root 5 ino 270 off 0 csum
>> 0x98f94189 expected csum 0x00000000 mirror 1
>> assertion failed: !memcmp_extent_buffer(b, &disk_key, offsetof(struct
>> btrfs_leaf, items[0].key), sizeof(disk_key)), file: fs/btrfs/ctree.c, line:
>> 2544
>> ------------[ cut here ]------------
>> kernel BUG at fs/btrfs/ctree.h:3500!
>> invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
>> RIP: 0010:btrfs_search_slot.cold.24+0x61/0x63 [btrfs]
>> Call Trace:
>> btrfs_lookup_csum+0x52/0x150 [btrfs]
>> __btrfs_lookup_bio_sums+0x209/0x640 [btrfs]
>> btrfs_submit_bio_hook+0x103/0x170 [btrfs]
>> submit_one_bio+0x59/0x80 [btrfs]
>> extent_read_full_page+0x58/0x80 [btrfs]
>> generic_file_read_iter+0x2f6/0x9d0
>> __vfs_read+0x14d/0x1a0
>> vfs_read+0x8d/0x140
>> ksys_read+0x52/0xc0
>> do_syscall_64+0x60/0x210
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> [CAUSE]
>> The fuzzed image has a corrupted leaf whose first key doesn't match with its
>> parent:
>> checksum tree key (CSUM_TREE ROOT_ITEM 0)
>> node 29741056 level 1 items 14 free 107 generation 19 owner CSUM_TREE
>> fs uuid 3381d111-94a3-4ac7-8f39-611bbbdab7e6
>> chunk uuid 9af1c3c7-2af5-488b-8553-530bd515f14c
>> ...
>> key (EXTENT_CSUM EXTENT_CSUM 79691776) block 29761536 gen 19
>>
>> leaf 29761536 items 1 free space 1726 generation 19 owner CSUM_TREE
>> leaf 29761536 flags 0x1(WRITTEN) backref revision 1
>> fs uuid 3381d111-94a3-4ac7-8f39-611bbbdab7e6
>> chunk uuid 9af1c3c7-2af5-488b-8553-530bd515f14c
>> item 0 key (EXTENT_CSUM EXTENT_CSUM 8798638964736) itemoff 1751
>> itemsize 2244
>> range start 8798638964736 end 8798641262592 length 2297856
>>
>> For the first time tree read, it will not pass verify_level_key() check.
>> But the extent buffer will still be cached.
>>
>> Also there is a pitfall in read_block_for_search(), where a cached
>> extent buffer will not be checked for its level and first key.
>>
>> There are context where we read tree block without verifying its
>> first key, such as scrub.
>>
>> So in that case, a corrupted leaf can sneak in and screw up the kernel.
>>
>> [FIX]
>> Export verify_level_key() as btrfs_verify_level_key() and call it in
>> read_block_for_search() to fill the hole.
>>
>> Please note, this will cause a lot of extra error message if we have a
>> bad tree block in any hot tree, but it's still much better to trigger
>> the final safe net in key_search_validate().
>>
>> Reported-by: Yoon Jungyeon <[email protected]>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202755
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202757
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202759
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202761
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202767
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202769
>> Signed-off-by: Qu Wenruo <[email protected]>
>
> Additionally which of those 6 issues contain the image which triggers
> this problem or all of them ?
The first contains the image which triggers the exact bug described in
[BUG] section.
The remaining images triggers the same first_key-mismatch-but-cached
problem, and can be rejected by this patch.
Thanks,
Qu
>
>> ---
>> There is one remaining report where I can't get any kernel message
>> before the VM completely lost reponse.
>> https://bugzilla.kernel.org/show_bug.cgi?id=202763
>> (out-of-bound access in end_bio_extent_readpage() when mounting and
>> operating a crafted btrfs image)
>>
>> And the above case can't be fixed by this patch. Still trying to get a
>> good idea of what's going wrong (AKA good kernel message).
>>
>> There is also another report, which doesn't provide the fuzzed image.
>> https://bugzilla.kernel.org/show_bug.cgi?id=202765
>> (NULL pointer dereference when mounting a crafted btrfs image)
>> ---
>> fs/btrfs/ctree.c | 10 ++++++++++
>> fs/btrfs/disk-io.c | 10 +++++-----
>> fs/btrfs/disk-io.h | 3 +++
>> 3 files changed, 18 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>> index 5a6c39b44c84..37447a7c5b4d 100644
>> --- a/fs/btrfs/ctree.c
>> +++ b/fs/btrfs/ctree.c
>> @@ -2401,6 +2401,16 @@ read_block_for_search(struct btrfs_root *root, struct
>> btrfs_path *p,
>> if (tmp) {
>> /* first we do an atomic uptodate check */
>> if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
>> + /*
>> + * Do extra check for first_key, as it's possible the
>> + * eb is read from the context without first_key
>> + * requirement
>> + */
>> + if (btrfs_verify_level_key(fs_info, tmp,
>> + parent_level - 1, &first_key, gen)) {
>> + free_extent_buffer(tmp);
>> + return -EUCLEAN;
>> + }
>> *eb_ret = tmp;
>> return 0;
>> }
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index 298b34721bc0..e2a0cb362d28 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -423,9 +423,9 @@ static int btrfs_check_super_csum(struct btrfs_fs_info
>> *fs_info,
>> return ret;
>> }
>>
>> -static int verify_level_key(struct btrfs_fs_info *fs_info,
>> - struct extent_buffer *eb, int level,
>> - struct btrfs_key *first_key, u64 parent_transid)
>> +int btrfs_verify_level_key(struct btrfs_fs_info *fs_info,
>> + struct extent_buffer *eb, int level,
>> + struct btrfs_key *first_key, u64 parent_transid)
>> {
>> int found_level;
>> struct btrfs_key found_key;
>> @@ -500,8 +500,8 @@ static int btree_read_extent_buffer_pages(struct
>> btrfs_fs_info *fs_info,
>> if (verify_parent_transid(io_tree, eb,
>> parent_transid, 0))
>> ret = -EIO;
>> - else if (verify_level_key(fs_info, eb, level,
>> - first_key, parent_transid))
>> + else if (btrfs_verify_level_key(fs_info, eb, level,
>> + first_key, parent_transid))
>> ret = -EUCLEAN;
>> else
>> break;
>> diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
>> index 987a64bc0c66..67a9fe2d29c7 100644
>> --- a/fs/btrfs/disk-io.h
>> +++ b/fs/btrfs/disk-io.h
>> @@ -39,6 +39,9 @@ static inline u64 btrfs_sb_offset(int mirror)
>> struct btrfs_device;
>> struct btrfs_fs_devices;
>>
>> +int btrfs_verify_level_key(struct btrfs_fs_info *fs_info,
>> + struct extent_buffer *eb, int level,
>> + struct btrfs_key *first_key, u64 parent_transid);
>> struct extent_buffer *read_tree_block(struct btrfs_fs_info *fs_info, u64
>> bytenr,
>> u64 parent_transid, int level,
>> struct btrfs_key *first_key);
>>
