==================================================================
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 ffff88812642f20c by task kworker/u4:0/8

CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 6.1.138-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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+0x71/0x210 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:427
 kasan_report+0x122/0x150 mm/kasan/report.c:531
 __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+0x1dc/0x6060 fs/ext4/extents.c:4165
 ext4_map_blocks+0x9cb/0x1b60 fs/ext4/inode.c:679
 mpage_map_one_extent fs/ext4/inode.c:2434 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2487 [inline]
 ext4_writepages+0x1230/0x2f70 fs/ext4/inode.c:2855
 do_writepages+0x3a9/0x5e0 mm/page-writeback.c:2491
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1612
 writeback_sb_inodes+0x9b8/0x1550 fs/fs-writeback.c:1903
 wb_writeback+0x3e9/0x970 fs/fs-writeback.c:2077
 wb_do_writeback fs/fs-writeback.c:2220 [inline]
 wb_workfn+0x350/0xda0 fs/fs-writeback.c:2260
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2292
 worker_thread+0xa26/0x11e0 kernel/workqueue.c:2439
 kthread+0x281/0x320 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0004990bc0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12642f
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 507, tgid 507 (syz-executor), ts 52868988298, free_ts 52961356982
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1d0/0x1f0 mm/page_alloc.c:2532
 prep_new_page mm/page_alloc.c:2539 [inline]
 get_page_from_freelist+0x2e63/0x2ef0 mm/page_alloc.c:4328
 __alloc_pages+0x235/0x4b0 mm/page_alloc.c:5606
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5638
 __folio_alloc_node include/linux/gfp.h:246 [inline]
 folio_alloc include/linux/gfp.h:275 [inline]
 alloc_page_vma include/linux/gfp.h:284 [inline]
 do_cow_fault mm/memory.c:4650 [inline]
 do_fault+0x3ec/0x17b0 mm/memory.c:4762
 handle_pte_fault mm/memory.c:5031 [inline]
 __handle_mm_fault mm/memory.c:5173 [inline]
 handle_mm_fault+0x14e9/0x23d0 mm/memory.c:5294
 do_user_addr_fault+0x530/0xaf0 arch/x86/mm/fault.c:1340
 handle_page_fault arch/x86/mm/fault.c:1431 [inline]
 exc_page_fault+0x51/0xb0 arch/x86/mm/fault.c:1487
 asm_exc_page_fault+0x27/0x30 arch/x86/include/asm/idtentry.h:608
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1459 [inline]
 free_pcp_prepare mm/page_alloc.c:1532 [inline]
 free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3384
 free_unref_page_list+0xba/0x7c0 mm/page_alloc.c:3525
 release_pages+0xad1/0xb20 mm/swap.c:1035
 free_pages_and_swap_cache+0x86/0xa0 mm/swap_state.c:314
 tlb_batch_pages_flush mm/mmu_gather.c:59 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:254 [inline]
 tlb_flush_mmu mm/mmu_gather.c:261 [inline]
 tlb_finish_mmu+0x1aa/0x370 mm/mmu_gather.c:361
 exit_mmap+0x31f/0x750 mm/mmap.c:3250
 __mmput+0x93/0x320 kernel/fork.c:1200
 mmput+0x47/0x60 kernel/fork.c:1222
 exit_mm kernel/exit.c:565 [inline]
 do_exit+0x957/0x2410 kernel/exit.c:858
 do_group_exit+0x210/0x2d0 kernel/exit.c:1021
 get_signal+0x13b5/0x1520 kernel/signal.c:2871
 arch_do_signal_or_restart+0xb0/0x1030 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87

Memory state around the buggy address:
 ffff88812642f100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812642f180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812642f200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff88812642f280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812642f300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 11486460536422: comm kworker/u4:0: lblock 0 mapped to illegal pblock 11486460536422 (length 1)
EXT4-fs (loop2): Delayed block allocation failed for inode 15 at logical offset 0 with max blocks 1 with error 117
EXT4-fs (loop2): This should not happen!! Data will be lost