[PATCH AUTOSEL 5.3 200/203] btrfs: extent-tree: Make sure we only allocate extents from block groups with the same type

Sasha Levin
2019-09-22T19:30:32Z

From: Qu Wenruo <wqu@suse.com>

[ Upstream commit 2a28468e525f3924efed7f29f2bc5a2926e7e19a ]

[BUG]
With fuzzed image and MIXED_GROUPS super flag, we can hit the following
BUG_ON():

kernel BUG at fs/btrfs/delayed-ref.c:491!
invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
CPU: 0 PID: 1849 Comm: sync Tainted: G O 5.2.0-custom #27
RIP: 0010:update_existing_head_ref.cold+0x44/0x46 [btrfs]
Call Trace:
add_delayed_ref_head+0x20c/0x2d0 [btrfs]
btrfs_add_delayed_tree_ref+0x1fc/0x490 [btrfs]
btrfs_free_tree_block+0x123/0x380 [btrfs]
__btrfs_cow_block+0x435/0x500 [btrfs]
btrfs_cow_block+0x110/0x240 [btrfs]
btrfs_search_slot+0x230/0xa00 [btrfs]
? __lock_acquire+0x105e/0x1e20
btrfs_insert_empty_items+0x67/0xc0 [btrfs]
alloc_reserved_file_extent+0x9e/0x340 [btrfs]
__btrfs_run_delayed_refs+0x78e/0x1240 [btrfs]
? kvm_clock_read+0x18/0x30
? __sched_clock_gtod_offset+0x21/0x50
btrfs_run_delayed_refs.part.0+0x4e/0x180 [btrfs]
btrfs_run_delayed_refs+0x23/0x30 [btrfs]
btrfs_commit_transaction+0x53/0x9f0 [btrfs]
btrfs_sync_fs+0x7c/0x1c0 [btrfs]
? __ia32_sys_fdatasync+0x20/0x20
sync_fs_one_sb+0x23/0x30
iterate_supers+0x95/0x100
ksys_sync+0x62/0xb0
__ia32_sys_sync+0xe/0x20
do_syscall_64+0x65/0x240
entry_SYSCALL_64_after_hwframe+0x49/0xbe

[CAUSE]
This situation is caused by several factors:
- Fuzzed image
The extent tree of this fs missed one backref for extent tree root.
So we can allocated space from that slot.

- MIXED_BG feature
Super block has MIXED_BG flag.

- No mixed block groups exists
All block groups are just regular ones.

This makes data space_info->block_groups[] contains metadata block
groups. And when we reserve space for data, we can use space in
metadata block group.

Then we hit the following file operations:

- fallocate
We need to allocate data extents.
find_free_extent() choose to use the metadata block to allocate space
from, and choose the space of extent tree root, since its backref is
missing.

This generate one delayed ref head with is_data = 1.

- extent tree update
We need to update extent tree at run_delayed_ref time.

This generate one delayed ref head with is_data = 0, for the same
bytenr of old extent tree root.

Then we trigger the BUG_ON().

[FIX]
The quick fix here is to check block_group->flags before using it.

The problem can only happen for MIXED_GROUPS fs. Regular filesystems
won't have space_info with DATA|METADATA flag, and no way to hit the
bug.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203255
Reported-by: Jungyeon Yoon <jungyeon.yoon@gmail.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/extent-tree.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 8b7eb22d508a5..ef2f80825c826 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5751,6 +5751,14 @@ static noinline int find_free_extent(struct btrfs_fs_info *fs_info,
*/
if ((flags & extra) && !(block_group->flags & extra))
goto loop;
+
+ /*
+ * This block group has different flags than we want.
+ * It's possible that we have MIXED_GROUP flag but no
+ * block group is mixed. Just skip such block group.
+ */
+ btrfs_release_block_group(block_group, delalloc);
+ continue;
}

have_block_group:
--
2.20.1