loop2: detected capacity change from 0 to 128
VFS: Found a Xenix FS (block size = 1024) on device loop2
==================================================================
BUG: KASAN: use-after-free in sysv_new_block+0x790/0x970 fs/sysv/balloc.c:113
Read of size 4 at addr ffff88805603a0c8 by task syz.2.3826/14683

CPU: 1 UID: 0 PID: 14683 Comm: syz.2.3826 Not tainted 6.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x16e/0x5b0 mm/kasan/report.c:521
 kasan_report+0x143/0x180 mm/kasan/report.c:634
 sysv_new_block+0x790/0x970 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:135 [inline]
 get_block+0x30a/0x16e0 fs/sysv/itree.c:254
 __block_write_begin_int+0x694/0x19a0 fs/buffer.c:2116
 sysv_make_empty+0xa8/0x640 fs/sysv/dir.c:262
 sysv_mkdir+0x7f/0x130 fs/sysv/namei.c:130
 vfs_mkdir+0x2fb/0x4f0 fs/namei.c:4313
 do_mkdirat+0x264/0x3a0 fs/namei.c:4336
 __do_sys_mkdirat fs/namei.c:4351 [inline]
 __se_sys_mkdirat fs/namei.c:4349 [inline]
 __x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4349
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd8b1b8b9d7
Code: 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 02 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd8b2acde68 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007fd8b2acdef0 RCX: 00007fd8b1b8b9d7
RDX: 00000000000001ff RSI: 0000400000000080 RDI: 00000000ffffff9c
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000400000000080
R13: 00007fd8b2acdeb0 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x7f54ac425 pfn:0x5603a
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f0(buddy)
raw: 00fff00000000000 ffffea000146cb48 ffffea0001621988 0000000000000000
raw: 00000007f54ac425 0000000000000000 00000000f0000000 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 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO), pid 14604, tgid 14602 (syz.3.3786), ts 525956878962, free_ts 526162363847
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0x365c/0x37a0 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x292/0x710 mm/page_alloc.c:4740
 alloc_pages_mpol+0x311/0x660 mm/mempolicy.c:2270
 folio_alloc_mpol_noprof mm/mempolicy.c:2289 [inline]
 vma_alloc_folio_noprof+0x12b/0x260 mm/mempolicy.c:2324
 folio_prealloc+0x2e/0x170
 alloc_anon_folio mm/memory.c:4834 [inline]
 do_anonymous_page mm/memory.c:4891 [inline]
 do_pte_missing mm/memory.c:4057 [inline]
 handle_pte_fault mm/memory.c:5888 [inline]
 __handle_mm_fault+0x32e6/0x6ef0 mm/memory.c:6031
 handle_mm_fault+0x3e5/0x8d0 mm/memory.c:6200
 do_user_addr_fault arch/x86/mm/fault.c:1337 [inline]
 handle_page_fault arch/x86/mm/fault.c:1480 [inline]
 exc_page_fault+0x459/0x8b0 arch/x86/mm/fault.c:1538
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
page last free pid 14604 tgid 14602 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_unref_folios+0xe40/0x18b0 mm/page_alloc.c:2707
 folios_put_refs+0x76c/0x860 mm/swap.c:994
 free_pages_and_swap_cache+0x2e5/0x690 mm/swap_state.c:331
 __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
 tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:389 [inline]
 tlb_flush_mmu+0x3a3/0x680 mm/mmu_gather.c:396
 tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:488
 vms_clear_ptes+0x432/0x530 mm/vma.c:1144
 vms_complete_munmap_vmas+0x210/0x8f0 mm/vma.c:1186
 do_vmi_align_munmap+0x5ef/0x6f0 mm/vma.c:1445
 do_vmi_munmap+0x24e/0x2d0 mm/vma.c:1493
 __vm_munmap+0x372/0x510 mm/vma.c:2955
 __do_sys_munmap mm/mmap.c:1084 [inline]
 __se_sys_munmap mm/mmap.c:1081 [inline]
 __x64_sys_munmap+0x60/0x70 mm/mmap.c:1081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888056039f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88805603a000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88805603a080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff88805603a100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805603a180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================