==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff88804aae5c70 by task kworker/u8:13/3817

CPU: 0 UID: 0 PID: 3817 Comm: kworker/u8:13 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: writeback wb_workfn (flush-7:2)
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 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:841 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x278/0x69c0 fs/ext4/extents.c:4208
 ext4_map_create_blocks fs/ext4/inode.c:613 [inline]
 ext4_map_blocks+0x82c/0x16f0 fs/ext4/inode.c:816
 mpage_map_one_extent fs/ext4/inode.c:2380 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2474 [inline]
 ext4_do_writepages+0x2213/0x44f0 fs/ext4/inode.c:2932
 ext4_writepages+0x203/0x350 fs/ext4/inode.c:3026
 do_writepages+0x32e/0x550 mm/page-writeback.c:2598
 __writeback_single_inode+0x133/0x1240 fs/fs-writeback.c:1737
 writeback_sb_inodes+0x8c8/0x1840 fs/fs-writeback.c:2030
 wb_writeback+0x42b/0xaa0 fs/fs-writeback.c:2216
 wb_do_writeback fs/fs-writeback.c:2363 [inline]
 wb_workfn+0x3fe/0xee0 fs/fs-writeback.c:2403
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xa08 pfn:0x4aae5
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea0000fe0248 ffffea000124b2c8 0000000000000000
raw: 0000000000000a08 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 8285, tgid 8284 (syz.6.309), ts 276487949880, free_ts 276789332866
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
 prep_new_page mm/page_alloc.c:1854 [inline]
 get_page_from_freelist+0x28c0/0x2960 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x39/0xe0 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1890 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1932 [inline]
 shmem_get_folio_gfp+0x633/0x1a70 mm/shmem.c:2556
 shmem_get_folio mm/shmem.c:2662 [inline]
 shmem_write_begin+0x166/0x320 mm/shmem.c:3315
 generic_perform_write+0x29d/0x8c0 mm/filemap.c:4314
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3490
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d5/0xb40 fs/read_write.c:686
 ksys_write+0x14b/0x260 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 8285 tgid 8284 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 free_unref_folios+0xc28/0x1810 mm/page_alloc.c:3000
 folios_put_refs+0x569/0x670 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
 __dentry_kill+0x209/0x660 fs/dcache.c:670
 finish_dput+0xc9/0x480 fs/dcache.c:879
 __fput+0x69d/0xa80 fs/file_table.c:476
 fput_close_sync+0x113/0x220 fs/file_table.c:573
 __do_sys_close fs/open.c:1573 [inline]
 __se_sys_close fs/open.c:1558 [inline]
 __x64_sys_close+0x7f/0x110 fs/open.c:1558
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804aae5b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804aae5b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804aae5c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff88804aae5c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804aae5d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================