On 12.03.19 г. 9:57 ч., 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(). >> <snip> >> 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; > > Actually why is the buffer still held when we return EUCLEAN since in > read_tree_block if btree_read_extent_buffer_pages returns an error > free_extent_buffer should be called and it should delete the eb from eb > cache, no ? IMO the correct behavior should be to remove the corrupted > buffer ASAP and not rely on later validation. Actually in this case the call to free_extent_buffer in read_tree_block won't really clean the buffer since at this point the buffer has refs = 2 (one from alloc_extent_buffer and one from being added to the tree), however the code in free_extent_buffer won't execute the atomic_cmpxchg to do the decrement nor will it execute the fix up right after the spinlock if (refs==2 && EXTENT_BUFFER_STALE) which leaves only a single call to atomic_dec_and_test in release_extent_buffer which will return false. That's wrong. The way to fix it is to either: a) add a call to atomic_dec(eb->refs) so that the single call to atomic_dec_and_test frees the eb b) call free_extent_buffer_stale which does atomic_dec itself, I'm more inclined to use this option. > >> 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); >> >
