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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
Read of size 4 at addr ffff88814c169018 by task kworker/u4:11/3983

CPU: 1 PID: 3983 Comm: kworker/u4:11 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: writeback wb_workfn (flush-7:2)
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
 ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x1da/0x6080 fs/ext4/extents.c:4166
 ext4_map_blocks+0x9cb/0x1b60 fs/ext4/inode.c:679
 mpage_map_one_extent fs/ext4/inode.c:2435 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2488 [inline]
 ext4_writepages+0x1260/0x3020 fs/ext4/inode.c:2856
 do_writepages+0x3a9/0x5e0 mm/page-writeback.c:2494
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1622
 writeback_sb_inodes+0x9b8/0x1550 fs/fs-writeback.c:1913
 wb_writeback+0x3f1/0x980 fs/fs-writeback.c:2089
 wb_do_writeback fs/fs-writeback.c:2236 [inline]
 wb_workfn+0x350/0xda0 fs/fs-writeback.c:2276
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0005305a40 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x14c169
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000001 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 4400, tgid 4399 (syz.9.1015), ts 273266890387, free_ts 274192962958
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2643
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2650
 get_page_from_freelist+0x2c7b/0x2cf0 mm/page_alloc.c:4554
 __alloc_pages+0x1c3/0x450 mm/page_alloc.c:5868
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5900
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 shmem_alloc_folio mm/shmem.c:1601 [inline]
 shmem_alloc_and_acct_folio+0x650/0x870 mm/shmem.c:1626
 shmem_get_folio_gfp+0x119f/0x2230 mm/shmem.c:1955
 shmem_get_folio mm/shmem.c:2086 [inline]
 shmem_write_begin+0xea/0x2c0 mm/shmem.c:2571
 generic_perform_write+0x2f6/0x6d0 mm/filemap.c:3887
 __generic_file_write_iter+0x227/0x580 mm/filemap.c:4016
 generic_file_write_iter+0xae/0x310 mm/filemap.c:4048
 __kernel_write_iter+0x27e/0x640 fs/read_write.c:517
 dump_emit_page fs/coredump.c:886 [inline]
 dump_user_range+0x3da/0x600 fs/coredump.c:913
 elf_core_dump+0x29e7/0x2ef0 fs/binfmt_elf.c:2354
 do_coredump+0x1557/0x21b0 fs/coredump.c:760
 get_signal+0x11db/0x1520 kernel/signal.c:2875
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1551 [inline]
 free_pcp_prepare mm/page_alloc.c:1625 [inline]
 free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3589
 free_unref_page_list+0x112/0x8b0 mm/page_alloc.c:3740
 release_pages+0xad1/0xb20 mm/swap.c:1047
 __pagevec_release+0x71/0xe0 mm/swap.c:1067
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x51a/0x1470 mm/shmem.c:955
 shmem_truncate_range mm/shmem.c:1071 [inline]
 shmem_evict_inode+0x242/0xa10 mm/shmem.c:1180
 evict+0x493/0x890 fs/inode.c:708
 iput_final fs/inode.c:1844 [inline]
 iput+0x620/0x670 fs/inode.c:1870
 do_unlinkat+0x375/0x6b0 fs/namei.c:4404
 __do_sys_unlink fs/namei.c:4445 [inline]
 __se_sys_unlink fs/namei.c:4443 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4443
 x64_sys_call+0x958/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff88814c168f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88814c168f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88814c169000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88814c169080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88814c169100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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