From: Qu Wenruo wqu@suse.com
commit 448de471cd4cab0cedd15770082567a69a784a11 upstream.
[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 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 the 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 if 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.
Furthermore, 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 the above reasons, a corrupted extent buffer can sneak into the buffer cache.
[FIX] Call verify_level_key in read_block_for_search to do another verification. For that purpose the function is exported.
Due to above reasons, although we can free corrupted extent buffer from cache, we still need the check in read_block_for_search(), for scrub and shared tree blocks.
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 Reported-by: Yoon Jungyeon jungyeon@gatech.edu CC: stable@vger.kernel.org # 4.19+ Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/ctree.c | 10 ++++++++++ fs/btrfs/disk-io.c | 10 +++++----- fs/btrfs/disk-io.h | 3 +++ 3 files changed, 18 insertions(+), 5 deletions(-)
--- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2416,6 +2416,16 @@ read_block_for_search(struct btrfs_root 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; + } *eb_ret = tmp; return 0; } --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -414,9 +414,9 @@ static int btrfs_check_super_csum(struct 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; @@ -493,8 +493,8 @@ static int btree_read_extent_buffer_page 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; --- a/fs/btrfs/disk-io.h +++ b/fs/btrfs/disk-io.h @@ -39,6 +39,9 @@ static inline u64 btrfs_sb_offset(int mi 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);