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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xaea/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff8880771dc018 by task kworker/u8:20/6833

CPU: 0 UID: 0 PID: 6833 Comm: kworker/u8:20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
 ext4_find_extent+0xaea/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x283/0x58b0 fs/ext4/extents.c:4261
 ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
 ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:809
 ext4_convert_unwritten_extents+0x2be/0x5f0 fs/ext4/extents.c:5029
 ext4_convert_unwritten_io_end_vec+0xff/0x170 fs/ext4/extents.c:5069
 ext4_end_io_end+0xc7/0x410 fs/ext4/page-io.c:200
 ext4_do_flush_completed_IO fs/ext4/page-io.c:291 [inline]
 ext4_end_io_rsv_work+0x26a/0x340 fs/ext4/page-io.c:306
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
 worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x5617 pfn:0x771dc
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001dc76c8 ffffea0001dc7748 0000000000000000
raw: 0000000000005617 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 8164, tgid 8164 (syz.2.605), ts 332335895341, free_ts 337066046079
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2484
 folio_alloc_mpol_noprof+0x39/0x70 mm/mempolicy.c:2503
 shmem_alloc_folio mm/shmem.c:1930 [inline]
 shmem_alloc_and_add_folio+0x445/0xf80 mm/shmem.c:1972
 shmem_get_folio_gfp+0x5a9/0x1670 mm/shmem.c:2567
 shmem_get_folio mm/shmem.c:2673 [inline]
 shmem_write_begin+0x16c/0x330 mm/shmem.c:3327
 generic_perform_write+0x2e2/0x8f0 mm/filemap.c:4314
 shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3502
 __kernel_write_iter+0x41e/0x880 fs/read_write.c:621
 dump_emit_page fs/coredump.c:1299 [inline]
 dump_user_range+0xb89/0x12d0 fs/coredump.c:1373
 elf_core_dump+0x34c2/0x3ad0 fs/binfmt_elf.c:2109
 coredump_write+0x1216/0x1910 fs/coredump.c:1050
 do_coredump fs/coredump.c:1127 [inline]
 vfs_coredump+0x36a9/0x4280 fs/coredump.c:1201
 get_signal+0x1107/0x1330 kernel/signal.c:3019
page last free pid 5827 tgid 5827 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 free_unref_folios+0xed5/0x16d0 mm/page_alloc.c:3040
 folios_put_refs+0x789/0x8d0 mm/swap.c:1002
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x52c/0x1660 mm/shmem.c:1149
 shmem_truncate_range mm/shmem.c:1277 [inline]
 shmem_evict_inode+0x240/0x9e0 mm/shmem.c:1407
 evict+0x61e/0xb10 fs/inode.c:846
 filename_unlinkat+0x43f/0x610 fs/namei.c:5544
 __do_sys_unlink fs/namei.c:5575 [inline]
 __se_sys_unlink+0x2e/0x140 fs/namei.c:5572
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880771dbf00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880771dbf80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880771dc000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8880771dc080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880771dc100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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