==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:847 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xac5/0xca0 fs/ext4/extents.c:962
Read of size 4 at addr ffff888133cea018 by task kworker/u4:5/355

CPU: 1 PID: 355 Comm: kworker/u4:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: writeback wb_workfn (flush-7:6)
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 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:847 [inline]
 ext4_find_extent+0xac5/0xca0 fs/ext4/extents.c:962
 ext4_ext_map_blocks+0x207/0x6200 fs/ext4/extents.c:4228
 ext4_map_blocks+0x9d8/0x1b70 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+0x1409/0x30e0 fs/ext4/inode.c:2856
 do_writepages+0x3a4/0x5f0 mm/page-writeback.c:2494
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1622
 writeback_sb_inodes+0xa10/0x15d0 fs/fs-writeback.c:1913
 wb_writeback+0x40b/0x9d0 fs/fs-writeback.c:2089
 wb_do_writeback fs/fs-writeback.c:2236 [inline]
 wb_workfn+0x378/0xeb0 fs/fs-writeback.c:2276
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11e0 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:ffffea0004cf3a80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x133cea
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 2029, tgid 2027 (syz.2.346), ts 489680363547, free_ts 490019099020
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2672
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2679
 get_page_from_freelist+0x2d12/0x2d80 mm/page_alloc.c:4585
 __alloc_pages+0x1fa/0x610 mm/page_alloc.c:5926
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5959
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 shmem_alloc_folio mm/shmem.c:1597 [inline]
 shmem_alloc_and_acct_folio+0x6dd/0x8c0 mm/shmem.c:1622
 shmem_get_folio_gfp+0x119f/0x2230 mm/shmem.c:1951
 shmem_get_folio mm/shmem.c:2082 [inline]
 shmem_write_begin+0xea/0x2c0 mm/shmem.c:2567
 generic_perform_write+0x32d/0x740 mm/filemap.c:3914
 __generic_file_write_iter+0x17a/0x230 mm/filemap.c:4013
 generic_file_write_iter+0xae/0x310 mm/filemap.c:4042
 call_write_iter include/linux/fs.h:2282 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x603/0xce0 fs/read_write.c:584
 ksys_write+0x149/0x250 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:646
 x64_sys_call+0x27b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1580 [inline]
 free_pcp_prepare mm/page_alloc.c:1654 [inline]
 free_unref_page_prepare+0x7f8/0x800 mm/page_alloc.c:3620
 free_unref_page_list+0x117/0x8c0 mm/page_alloc.c:3771
 release_pages+0xc93/0xcf0 mm/swap.c:1053
 __pagevec_release+0x71/0xe0 mm/swap.c:1073
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x574/0x1540 mm/shmem.c:951
 shmem_truncate_range mm/shmem.c:1067 [inline]
 shmem_evict_inode+0x255/0xa50 mm/shmem.c:1176
 evict+0x4d7/0x8f0 fs/inode.c:708
 iput_final fs/inode.c:1844 [inline]
 iput+0x620/0x670 fs/inode.c:1870
 dentry_unlink_inode+0x33d/0x3f0 fs/dcache.c:405
 __dentry_kill+0x460/0x670 fs/dcache.c:611
 dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
 dput+0x42/0x80 fs/dcache.c:918
 __fput+0x5be/0x8f0 fs/file_table.c:328
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0x9b/0xb0 kernel/entry/common.c:177

Memory state around the buggy address:
 ffff888133ce9f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888133ce9f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888133cea000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888133cea080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888133cea100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop6): ext4_map_blocks:745: inode #18: block 77309411328000: comm kworker/u4:5: lblock 0 mapped to illegal pblock 77309411328000 (length 1)
EXT4-fs (loop6): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 1 with error 117
EXT4-fs (loop6): This should not happen!! Data will be lost