EXT4-fs (loop4): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:846 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:961
Read of size 4 at addr ffff88804a1d4e18 by task syz.4.206/6876

CPU: 1 UID: 0 PID: 6876 Comm: syz.4.206 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 ext4_ext_binsearch fs/ext4/extents.c:846 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:961
 ext4_insert_range+0x52e/0xb30 fs/ext4/extents.c:5627
 ext4_fallocate+0x352/0x3d0 fs/ext4/extents.c:4859
 vfs_fallocate+0x669/0x7e0 fs/open.c:339
 ksys_fallocate fs/open.c:363 [inline]
 __do_sys_fallocate fs/open.c:368 [inline]
 __se_sys_fallocate fs/open.c:366 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:366
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8318f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007f5a840ad038 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 00007f5a833e5fa0 RCX: 00007f5a8318f749
RDX: 0000000000000000 RSI: 0000000000000020 RDI: 0000000000000006
RBP: 00007f5a83213f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000008000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a833e6038 R14: 00007f5a833e5fa0 R15: 00007ffff446e0b8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x501c pfn:0x4a1d4
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00012874c8 ffffea0001287548 0000000000000000
raw: 000000000000501c 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 6828, tgid 6828 (syz.2.198), ts 179207352453, free_ts 183500256238
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1857
 prep_new_page mm/page_alloc.c:1865 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x39/0x70 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1902 [inline]
 shmem_alloc_and_add_folio+0x423/0xf40 mm/shmem.c:1944
 shmem_get_folio_gfp+0x59d/0x1660 mm/shmem.c:2568
 shmem_get_folio mm/shmem.c:2674 [inline]
 shmem_write_begin+0x16c/0x330 mm/shmem.c:3327
 generic_perform_write+0x2c5/0x900 mm/filemap.c:4314
 shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3502
 __kernel_write_iter+0x428/0x910 fs/read_write.c:619
 dump_emit_page fs/coredump.c:1298 [inline]
 dump_user_range+0x8a0/0xc90 fs/coredump.c:1372
 elf_core_dump+0x3369/0x3960 fs/binfmt_elf.c:2111
 coredump_write+0x1121/0x18b0 fs/coredump.c:1049
 do_coredump fs/coredump.c:1126 [inline]
 vfs_coredump+0x3321/0x3e60 fs/coredump.c:1200
 get_signal+0x1108/0x1340 kernel/signal.c:3019
page last free pid 5824 tgid 5824 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1406 [inline]
 free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:3000
 folios_put_refs+0x584/0x670 mm/swap.c:1002
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x49e/0x1490 mm/shmem.c:1137
 shmem_truncate_range mm/shmem.c:1249 [inline]
 shmem_evict_inode+0x26e/0xa70 mm/shmem.c:1379
 evict+0x5f4/0xae0 fs/inode.c:837
 do_unlinkat+0x41d/0x5d0 fs/namei.c:5509
 __do_sys_unlink fs/namei.c:5540 [inline]
 __se_sys_unlink fs/namei.c:5538 [inline]
 __x64_sys_unlink+0x47/0x50 fs/namei.c:5538
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804a1d4d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804a1d4d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804a1d4e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88804a1d4e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804a1d4f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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