==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
Read of size 4 at addr ffff88812fdca018 by task kworker/u4:0/7

CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0xe2/0x130 mm/kasan/report.c:452
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
 ext4_ext_map_blocks+0x20b/0x5dd0 fs/ext4/extents.c:4160
 ext4_map_blocks+0x985/0x1bd0 fs/ext4/inode.c:674
 mpage_map_one_extent fs/ext4/inode.c:2452 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2505 [inline]
 ext4_writepages+0x136a/0x2eb0 fs/ext4/inode.c:2873
 do_writepages+0x128/0x280 mm/page-writeback.c:2380
 __writeback_single_inode+0xd5/0xa20 fs/fs-writeback.c:1470
 writeback_sb_inodes+0x8ca/0x1480 fs/fs-writeback.c:1733
 wb_writeback+0x403/0xbe0 fs/fs-writeback.c:1908
 wb_do_writeback fs/fs-writeback.c:2053 [inline]
 wb_workfn+0x3ac/0xf30 fs/fs-writeback.c:2094
 process_one_work+0x6e1/0xba0 kernel/workqueue.c:2301
 worker_thread+0xa6a/0x13c0 kernel/workqueue.c:2447
 kthread+0x346/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

The buggy address belongs to the page:
page:ffffea0004bf7280 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12fdca
flags: 0x4000000000000000()
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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 1028, ts 43854248336, free_ts 43875842742
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x223b/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x290/0x620 mm/page_alloc.c:5370
 __alloc_pages include/linux/gfp.h:544 [inline]
 __alloc_pages_node include/linux/gfp.h:557 [inline]
 alloc_pages_node include/linux/gfp.h:571 [inline]
 alloc_pages include/linux/gfp.h:590 [inline]
 shmem_alloc_page+0x1fd/0x380 mm/shmem.c:1584
 shmem_alloc_and_acct_page+0x3b7/0x820 mm/shmem.c:1609
 shmem_getpage_gfp+0x625/0x2120 mm/shmem.c:1922
 shmem_getpage mm/shmem.c:165 [inline]
 shmem_write_begin+0xce/0x1b0 mm/shmem.c:2501
 generic_perform_write+0x2ce/0x540 mm/filemap.c:3509
 __generic_file_write_iter+0x24b/0x480 mm/filemap.c:3638
 generic_file_write_iter+0xa9/0x1d0 mm/filemap.c:3670
 call_write_iter include/linux/fs.h:2066 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x758/0xdc0 fs/read_write.c:605
 ksys_write+0x149/0x250 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 free_pcp_prepare mm/page_alloc.c:1421 [inline]
 free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336
 free_unref_page_list+0x129/0x9c0 mm/page_alloc.c:3443
 release_pages+0xe52/0xea0 mm/swap.c:1103
 __pagevec_release+0x71/0xe0 mm/swap.c:1123
 pagevec_release include/linux/pagevec.h:88 [inline]
 shmem_undo_range+0x74a/0x1810 mm/shmem.c:969
 shmem_truncate_range mm/shmem.c:1073 [inline]
 shmem_evict_inode+0x210/0xa00 mm/shmem.c:1173
 evict+0x4ae/0x930 fs/inode.c:612
 iput_final fs/inode.c:1736 [inline]
 iput+0x638/0x7c0 fs/inode.c:1762
 do_unlinkat+0x347/0x680 fs/namei.c:4050
 __do_sys_unlink fs/namei.c:4090 [inline]
 __se_sys_unlink fs/namei.c:4088 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4088
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Memory state around the buggy address:
 ffff88812fdc9f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812fdc9f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812fdca000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88812fdca080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812fdca100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs (loop0): Delayed block allocation failed for inode 18 at logical offset 168 with max blocks 8 with error 117
EXT4-fs (loop0): This should not happen!! Data will be lost