btrfs: relocation: Fix a KASAN report on btrfs_reloc_pre_snapshot() due to extended...

[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 btrfs_reloc_pre_snapshot+0x85/0xc0 [btrfs]
  Read of size 4 at addr ffff888157140100 by task btrfs/1822

  CPU: 2 PID: 1822 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
   check_memory_region+0x13c/0x1b0
   __asan_loadN+0xf/0x20
   btrfs_reloc_pre_snapshot+0x85/0xc0 [btrfs]
   create_pending_snapshot+0x209/0x15f0 [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]
Again, we try to access root->reloc_root without verify if that reloc
root is already dead (being freed).

[FIX]
Check if the root has dead reloc root before accessing it.

Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Signed-off-by: Qu Wenruo <wqu@suse.com>
(cherry picked from commit 6fcb3c241e81ef5812388a4ef81dc5c815f643d3)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 3e8d21d748bb0dcdd834d37f8a8d4e2a4bc2bb98..566c84d5f73c34539af990f24aa946996709e1f3 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4750,7 +4750,8 @@ void btrfs_reloc_pre_snapshot(struct btrfs_pending_snapshot *pending,
        struct btrfs_root *root = pending->root;
        struct reloc_control *rc = root->fs_info->reloc_ctl;
 
-       if (!root->reloc_root || !rc)
+       if (!root->reloc_root || !rc || test_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
+                               &root->state))
                return;
 
        if (!rc->merge_reloc_tree)