In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix qgroup reserve leaks in cow_file_range

In the buffered write path, the dirty page owns the qgroup reserve until
it creates an ordered_extent.

Therefore, any errors that occur before the ordered_extent is created
must free that reservation, or else the space is leaked. The fstest
generic/475 exercises various IO error paths, and is able to trigger
errors in cow_file_range where we fail to get to allocating the ordered
extent. Note that because we *do* clear delalloc, we are likely to
remove the inode from the delalloc list, so the inodes/pages to not have
invalidate/launder called on them in the commit abort path.

This results in failures at the unmount stage of the test that look like:

  BTRFS: error (device dm-8 state EA) in cleanup_transaction:2018: errno=-5 IO failure
  BTRFS: error (device dm-8 state EA) in btrfs_replace_file_extents:2416: errno=-5 IO failure
  BTRFS warning (device dm-8 state EA): qgroup 0/5 has unreleased space, type 0 rsv 28672
  ------------[ cut here ]------------
  WARNING: CPU: 3 PID: 22588 at fs/btrfs/disk-io.c:4333 close_ctree+0x222/0x4d0 [btrfs]
  Modules linked in: btrfs blake2b_generic libcrc32c xor zstd_compress raid6_pq
  CPU: 3 PID: 22588 Comm: umount Kdump: loaded Tainted: G W          6.10.0-rc7-gab56fde445b8 #21
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
  RIP: 0010:close_ctree+0x222/0x4d0 [btrfs]
  RSP: 0018:ffffb4465283be00 EFLAGS: 00010202
  RAX: 0000000000000001 RBX: ffffa1a1818e1000 RCX: 0000000000000001
  RDX: 0000000000000000 RSI: ffffb4465283bbe0 RDI: ffffa1a19374fcb8
  RBP: ffffa1a1818e13c0 R08: 0000000100028b16 R09: 0000000000000000
  R10: 0000000000000003 R11: 0000000000000003 R12: ffffa1a18ad7972c
  R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  FS:  00007f9168312b80(0000) GS:ffffa1a4afcc0000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f91683c9140 CR3: 000000010acaa000 CR4: 00000000000006f0
  Call Trace:
   <TASK>
   ? close_ctree+0x222/0x4d0 [btrfs]
   ? __warn.cold+0x8e/0xea
   ? close_ctree+0x222/0x4d0 [btrfs]
   ? report_bug+0xff/0x140
   ? handle_bug+0x3b/0x70
   ? exc_invalid_op+0x17/0x70
   ? asm_exc_invalid_op+0x1a/0x20
   ? close_ctree+0x222/0x4d0 [btrfs]
   generic_shutdown_super+0x70/0x160
   kill_anon_super+0x11/0x40
   btrfs_kill_super+0x11/0x20 [btrfs]
   deactivate_locked_super+0x2e/0xa0
   cleanup_mnt+0xb5/0x150
   task_work_run+0x57/0x80
   syscall_exit_to_user_mode+0x121/0x130
   do_syscall_64+0xab/0x1a0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  RIP: 0033:0x7f916847a887
  ---[ end trace 0000000000000000 ]---
  BTRFS error (device dm-8 state EA): qgroup reserved space leaked

Cases 2 and 3 in the out_reserve path both pertain to this type of leak
and must free the reserved qgroup data. Because it is already an error
path, I opted not to handle the possible errors in
btrfs_free_qgroup_data.

kernel.org https://git.kernel.org/stable/c/30479f31d44d47ed00ae0c7453d9b253537005b2 [No types assigned]

kernel.org https://git.kernel.org/stable/c/e42ef22bc10f0309c0c65d8d6ca8b4127a674b7f [No types assigned]