HPFS: dnode_end_de: dnode->first_free = 7b3184b6
==================================================================
BUG: KASAN: use-after-free in hpfs_count_dnodes+0x874/0xb70 fs/hpfs/dnode.c:773
Read of size 2 at addr ffff88806d4084d0 by task syz.1.18/6480

CPU: 0 UID: 0 PID: 6480 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 hpfs_count_dnodes+0x874/0xb70 fs/hpfs/dnode.c:773
 hpfs_read_inode+0xc79/0x1050 fs/hpfs/inode.c:128
 hpfs_fill_super+0x123d/0x1fa0 fs/hpfs/super.c:651
 get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
 vfs_get_tree+0x92/0x2a0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3758 [inline]
 do_new_mount+0x341/0xd30 fs/namespace.c:3834
 do_mount fs/namespace.c:4167 [inline]
 __do_sys_mount fs/namespace.c:4399 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4376
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7feea179b90a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007feea25a6e58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007feea25a6ee0 RCX: 00007feea179b90a
RDX: 000020000000a000 RSI: 0000200000009ec0 RDI: 00007feea25a6ea0
RBP: 000020000000a000 R08: 00007feea25a6ee0 R09: 0000000003200041
R10: 0000000003200041 R11: 0000000000000246 R12: 0000200000009ec0
R13: 00007feea25a6ea0 R14: 0000000000009e21 R15: 0000200000000000
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x31e pfn:0x6d408
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00017dfc08 ffffea00017d6888 0000000000000000
raw: 000000000000031e 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 6334, tgid 6334 (syz-executor), ts 119202934007, free_ts 119954130762
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
 prep_new_page mm/page_alloc.c:1866 [inline]
 get_page_from_freelist+0x24ba/0x2540 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
 alloc_pages_mpol+0x235/0x490 mm/mempolicy.c:2490
 folio_alloc_mpol_noprof+0x39/0x160 mm/mempolicy.c:2509
 vma_alloc_folio_noprof+0xe1/0x1e0 mm/mempolicy.c:2544
 folio_prealloc mm/memory.c:-1 [inline]
 do_cow_fault mm/memory.c:5960 [inline]
 do_fault mm/memory.c:6072 [inline]
 do_pte_missing+0x520/0x33f0 mm/memory.c:4550
 handle_pte_fault mm/memory.c:6454 [inline]
 __handle_mm_fault mm/memory.c:6592 [inline]
 handle_mm_fault+0x1bd7/0x3170 mm/memory.c:6761
 do_user_addr_fault+0xa73/0x1340 arch/x86/mm/fault.c:1334
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
page last free pid 6335 tgid 6335 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 free_unref_folios+0xcec/0x1480 mm/page_alloc.c:3004
 folios_put_refs+0x9ff/0xb40 mm/swap.c:1008
 free_pages_and_swap_cache+0x2b9/0x490 mm/swap_state.c:401
 __tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline]
 tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
 tlb_flush_mmu+0x6d3/0xa30 mm/mmu_gather.c:424
 tlb_finish_mmu+0xf9/0x230 mm/mmu_gather.c:549
 exit_mmap+0x498/0x9e0 mm/mmap.c:1313
 __mmput+0x118/0x430 kernel/fork.c:1178
 exit_mm+0x18e/0x250 kernel/exit.c:581
 do_exit+0x6a2/0x22c0 kernel/exit.c:963
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1117
 get_signal+0x1284/0x1330 kernel/signal.c:3037
 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:269 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:328 [inline]
 do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88806d408380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806d408400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88806d408480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                 ^
 ffff88806d408500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806d408580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================