CVE: CVE-2024-40962
Published: 2024-07-12
Description: In the Linux kernel, the following vulnerability has been resolved:

btrfs: zoned: allocate dummy checksums for zoned NODATASUM writes

Shin'ichiro reported that when he's running fstests' test-case
btrfs/167 on emulated zoned devices, he's seeing the following NULL
pointer dereference in 'btrfs_zone_finish_endio()':

  Oops: general protection fault, probably for non-canonical address 0xdffffc[PII_REDACTED]: 0000 [#1] PREEMPT SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x[PII_REDACTED]000088-0x[PII_REDACTED]00008f]
  CPU: 4 PID: 2332440 Comm: kworker/u80:15 Tainted: G        W          6.10.0-rc2-kts+ #4
  Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.3 02/21/2020
  Workqueue: btrfs-endio-write btrfs_work_helper [btrfs]
  RIP: 0010:btrfs_zone_finish_endio.part.0+0x34/0x160 [btrfs]

  RSP: 0018:ffff88867f107a90 EFLAGS: 00010206
  RAX: dffffc[PII_REDACTED] RBX: [PII_REDACTED] RCX: ffffffff893e5534
  RDX: [PII_REDACTED] RSI: [PII_REDACTED] RDI: [PII_REDACTED]
  RBP: [PII_REDACTED] R08: [PII_REDACTED] R09: ffffed[PII_REDACTED]
  R10: ffff88840b4b0143 R11: ffff88834dfff600 R12: ffff88840b4b0000
  R13: [PII_REDACTED] R14: [PII_REDACTED] R15: ffff888530ad5210
  FS:  [PII_REDACTED](0000) GS:ffff888e3f800000(0000) knlGS:[PII_REDACTED]
  CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
  CR2: 00007f87223fff38 CR3: 00000007a7c6a002 CR4:[PII_REDACTED]7706f0
  DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
  DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
  PKRU: 55555554
  Call Trace:
   <TASK>
   ? __die_body.cold+0x19/0x27
   ? die_addr+0x46/0x70
   ? exc_general_protection+0x14f/0x250
   ? asm_exc_general_protection+0x26/0x30
   ? do_raw_read_unlock+0x44/0x70
   ? btrfs_zone_finish_endio.part.0+0x34/0x160 [btrfs]
   btrfs_finish_one_ordered+0x5d9/0x19a0 [btrfs]
   ? __pfx_lock_release+0x10/0x10
   ? do_raw_write_lock+0x90/0x260
   ? __pfx_do_raw_write_lock+0x10/0x10
   ? __pfx_btrfs_finish_one_ordered+0x10/0x10 [btrfs]
   ? _raw_write_unlock+0x23/0x40
   ? btrfs_finish_ordered_zoned+0x5a9/0x850 [btrfs]
   ? lock_acquire+0x435/0x500
   btrfs_work_helper+0x1b1/0xa70 [btrfs]
   ? __schedule+0x10a8/0x60b0
   ? __pfx___might_resched+0x10/0x10
   process_one_work+0x862/0x1410
   ? __pfx_lock_acquire+0x10/0x10
   ? __pfx_process_one_work+0x10/0x10
   ? assign_work+0x16c/0x240
   worker_thread+0x5e6/0x1010
   ? __pfx_worker_thread+0x10/0x10
   kthread+0x2c3/0x3a0
   ? trace_irq_enable.constprop.0+0xce/0x110
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x31/0x70
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>

Enabling CONFIG_BTRFS_ASSERT revealed the following assertion to
trigger:

  assertion failed: !list_empty(&ordered->list), in fs/btrfs/zoned.c:1815

This indicates, that we're missing the checksums list on the
ordered_extent. As btrfs/167 is doing a NOCOW write this is to be
expected.

Further analysis with drgn confirmed the assumption:

  >>> inode = prog.crashed_thread().stack_trace()[11]['ordered'].inode
  >>> btrfs_inode = drgn.container_of(inode, "struct btrfs_inode", \
         				"vfs_inode")
  >>> print(btrfs_inode.flags)
  (u32)1

As zoned emulation mode simulates conventional zones on regular devices,
we cannot use zone-append for writing. But we're only attaching dummy
checksums if we're doing a zone-append write.

So for NOCOW zoned data writes on conventional zones, also attach a
dummy checksum.
CVSS Score: 5.5 (MEDIUM)
CWE: CWE-476
References: https://git.kernel.org/stable/c/082b3d4e788953a3ff42ecdb70c[PII_REDACTED]285; https://git.kernel.org/stable/c/25cfe59f4470a051d1b80f51fa0ca3a5048e4a19; https://git.kernel.org/stable/c/cebae292e0c32a228e8f2219c270a7237be24a6a