CVE-2024-40962

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

btrfs: zoned: allocate dummy checksums for zoned NODATASUM writes

Shinichiro reported that when hes running fstests test-case btrfs/167 on emulated zoned devices, hes seeing the following NULL pointer dereference in btrfs_zone_finish_endio():

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000011: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f] 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: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff893e5534 RDX: 0000000000000011 RSI: 0000000000000004 RDI: 0000000000000088 RBP: 0000000000000002 R08: 0000000000000001 R09: ffffed1081696028 R10: ffff88840b4b0143 R11: ffff88834dfff600 R12: ffff88840b4b0000 R13: 0000000000020000 R14: 0000000000000000 R15: ffff888530ad5210 FS: 0000000000000000(0000) GS:ffff888e3f800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f87223fff38 CR3: 00000007a7c6a002 CR4: 00000000007706f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: ? __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

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 were 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 were only attaching dummy checksums if were doing a zone-append write.

So for NOCOW zoned data writes on conventional zones, also attach a dummy checksum.

Weakness

The product dereferences a pointer that it expects to be valid but is NULL.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/082b3d4e788953a3ff42ecdb70c4210149076285
• https://git.kernel.org/stable/c/25cfe59f4470a051d1b80f51fa0ca3a5048e4a19
• https://git.kernel.org/stable/c/cebae292e0c32a228e8f2219c270a7237be24a6a
• https://git.kernel.org/stable/c/082b3d4e788953a3ff42ecdb70c4210149076285
• https://git.kernel.org/stable/c/25cfe59f4470a051d1b80f51fa0ca3a5048e4a19
• https://git.kernel.org/stable/c/cebae292e0c32a228e8f2219c270a7237be24a6a