On 2019/3/12 下午7:07, Nikolay Borisov wrote: > > > 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 <jungyeon@xxxxxxxxxx> >> 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 <wqu@xxxxxxxx> >> --- >> 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? Previous btrfs_buffer_uptodate() call implies verify_parent_transid() check, and that's why btrfs_buffer_uptodate() needs transid parameter. Thanks, Qu > >> *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); >>
