On 12.03.19 г. 11:10 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
>
> When reading above tree block, we have extent_buffer->refs = 2 in the
> context:
> - initial one from __alloc_extent_buffer()
> alloc_extent_buffer()
> |- __alloc_extent_buffer()
> |- atomic_set(&eb->refs, 1)
>
> - one being added to fs_info->buffer_radix
> alloc_extent_buffer()
> |- check_buffer_tree_ref()
> |- atomic_inc(&eb->refs)
>
> So even we call free_extent_buffer() in read_tree_block or other similar
> situation, we only decrease the refs by 1, it doesn't reach 0 and won't
> be freed right now.
>
> The staled eb and its corrupted content will still be kept cached.
>
> Further more, we have several extra cases where we either don't do
> first key check or the check is not proper for all callers:
> - scrub
> We just don't have first key in this context.
>
> - shared tree block
> One tree block can be shared by several snapshot/subvolume trees.
> In that case, the first key check for one subvolume doesn't apply to
> another.
>
> So for above reasons, a corrupted extent buffer can sneak into the
> buffer cache.
>
> [FIX]
> Export verify_level_key() as btrfs_verify_level_key() and call it in
> read_block_for_search() to fill the hole.
>
> Due to above described reasons, even we can free corrupted extent buffer
> from cache, we still need the check in read_block_for_search(), for
> scrub and shared tree blocks.
>
> 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]>
> ---
> changelog:
> v2:
> - Commit message update to show the reason why stale ebs are kept in
> cache.
> - Commit message update to show extra reasons why we still need the
> check, mainly for scrub and shared tree blocks.
> ---
> 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..7672932aa5b4 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, eb can be stale due to
> + * being cached, read from scrub, or have multiple
> + * parents (shared tree blocks).
> + */
> + if (btrfs_verify_level_key(fs_info, tmp,
> + parent_level - 1, &first_key, gen)) {
> + free_extent_buffer(tmp);
> + return -EUCLEAN;
> + }
What about verify_parent_transid? Shouldn't it also be checked here?
> *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);
>
