[BUG]
When running workload with balance start/cancel, snapshot
creation/deletion and fsstress, we can hit the following KASAN report:
==================================================================
BUG: KASAN: use-after-free in create_reloc_root+0x9f/0x460 [btrfs]
Read of size 8 at addr ffff8881571741f0 by task btrfs/3539
CPU: 6 PID: 3539 Comm: btrfs Tainted: G O 5.5.0-rc1-custom+ #40
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
dump_stack+0xc2/0x11a
print_address_description.constprop.0+0x20/0x210
__kasan_report.cold+0x1b/0x41
kasan_report+0x12/0x20
__asan_load8+0x54/0x90
create_reloc_root+0x9f/0x460 [btrfs]
btrfs_reloc_post_snapshot+0xff/0x6c0 [btrfs]
create_pending_snapshot+0xa9b/0x15f0 [btrfs]
create_pending_snapshots+0x111/0x140 [btrfs]
btrfs_commit_transaction+0x7a6/0x1360 [btrfs]
btrfs_mksubvol+0x915/0x960 [btrfs]
btrfs_ioctl_snap_create_transid+0x1d5/0x1e0 [btrfs]
btrfs_ioctl_snap_create_v2+0x1d3/0x270 [btrfs]
btrfs_ioctl+0x241b/0x3e60 [btrfs]
do_vfs_ioctl+0x831/0xb10
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x43/0x50
do_syscall_64+0x79/0xe0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
[CAUSE]
This is another case where root->reloc_root is accessed without checking
if the reloc root is already dead.
[FIX]
Also check DEAD_RELOC_TREE bit before accessing root->reloc_root.
Reported-by: Zygo Blaxell <ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx>
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
fs/btrfs/relocation.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index bb41b981e493..619ccb183515 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4755,7 +4755,14 @@ int btrfs_reloc_post_snapshot(struct btrfs_trans_handle *trans,
struct reloc_control *rc = root->fs_info->reloc_ctl;
int ret;
- if (!root->reloc_root || !rc)
+ /*
+ * We don't need to use reloc tree if:
+ * - No reloc tree
+ * - Relocation not running
+ * - Reloc tree already merged
+ */
+ if (!root->reloc_root || !rc || test_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
+ &root->state))
return 0;
rc = root->fs_info->reloc_ctl;
--
2.24.0
