==================================================================
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 ffff88812fd13018 by task kworker/u4:2/43

CPU: 1 PID: 43 Comm: kworker/u4:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: writeback wb_workfn (flush-7:2)
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:837 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x207/0x61d0 fs/ext4/extents.c:4166
 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:ffffea0004bf44c0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12fd13
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004bf44c8 ffffea0004bf44c8 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff88812fd12f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812fd12f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812fd13000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^