==================================================================
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 ffff8881325818e8 by task kworker/u4:0/8

CPU: 0 PID: 8 Comm: kworker/u4:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: writeback wb_workfn (flush-7:3)
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+0x71/0x200 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+0x1da/0x6080 fs/ext4/extents.c:4166
 ext4_map_blocks+0x9cb/0x1b60 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+0x1260/0x3020 fs/ext4/inode.c:2856
 do_writepages+0x3a9/0x5e0 mm/page-writeback.c:2494
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1622
 writeback_sb_inodes+0x9b8/0x1550 fs/fs-writeback.c:1913
 wb_writeback+0x3f1/0x980 fs/fs-writeback.c:2089
 wb_do_writeback fs/fs-writeback.c:2236 [inline]
 wb_workfn+0x350/0xda0 fs/fs-writeback.c:2276
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11f0 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:ffffea0004c96040 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x132581
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004867408 ffffea0004d684c8 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 986, tgid 976 (syz.4.154), ts 54506904639, free_ts 54817187848
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2643
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2650
 get_page_from_freelist+0x2c7b/0x2cf0 mm/page_alloc.c:4554
 __alloc_pages+0x1c3/0x450 mm/page_alloc.c:5868
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5900
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 shmem_alloc_folio mm/shmem.c:1601 [inline]
 shmem_alloc_and_acct_folio+0x650/0x870 mm/shmem.c:1626
 shmem_get_folio_gfp+0x119f/0x2230 mm/shmem.c:1955
 shmem_fault+0x1ae/0x650 mm/shmem.c:2170
 __do_fault mm/memory.c:4373 [inline]
 do_read_fault mm/memory.c:4739 [inline]
 do_fault+0x1a6f/0x1df0 mm/memory.c:4875
 handle_pte_fault mm/memory.c:5171 [inline]
 __handle_mm_fault mm/memory.c:5313 [inline]
 handle_mm_fault+0x12fa/0x2640 mm/memory.c:5453
 faultin_page mm/gup.c:1026 [inline]
 __get_user_pages+0x33d/0xd80 mm/gup.c:1250
 populate_vma_page_range mm/gup.c:1607 [inline]
 __mm_populate+0x2e4/0x420 mm/gup.c:1721
 mm_populate include/linux/mm.h:3148 [inline]
 vm_mmap_pgoff+0x268/0x3f0 mm/util.c:530
 ksys_mmap_pgoff+0xf6/0x1d0 mm/mmap.c:1536
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:93 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline]
 __x64_sys_mmap+0xfa/0x110 arch/x86/kernel/sys_x86_64.c:86
 x64_sys_call+0x8fd/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:10
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1551 [inline]
 free_pcp_prepare mm/page_alloc.c:1625 [inline]
 free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3589
 free_unref_page_list+0x112/0x8b0 mm/page_alloc.c:3740
 release_pages+0xad1/0xb20 mm/swap.c:1047
 __pagevec_release+0x71/0xe0 mm/swap.c:1067
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x51a/0x1470 mm/shmem.c:955
 shmem_truncate_range mm/shmem.c:1071 [inline]
 shmem_evict_inode+0x242/0xa10 mm/shmem.c:1180
 evict+0x493/0x890 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+0x1db/0x240 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:
 ffff888132581780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888132581800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888132581880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                          ^
 ffff888132581900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888132581980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:3187!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8 Comm: kworker/u4:0 Tainted: G    B              syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: writeback wb_workfn (flush-7:3)
RIP: 0010:ext4_split_extent_at+0xf3f/0xf60 fs/ext4/extents.c:3187
Code: ff ff 44 89 f1 80 e1 07 fe c1 38 c1 0f 8c 45 fb ff ff 4c 89 f7 49 89 f7 e8 fe 5f d0 ff 4c 89 fe e9 32 fb ff ff e8 d1 e7 8b ff <0f> 0b e8 ca e7 8b ff 0f 0b e8 c3 e7 8b ff 0f 0b e8 bc e7 8b ff 0f
RSP: 0018:ffffc90000086ac0 EFLAGS: 00010293
RAX: ffffffff81e4409f RBX: 0000000000000000 RCX: ffff888100298000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000086c30 R08: 0000000000000010 R09: 000000000000043b
R10: ffffed102384ea2a R11: 1ffff1102384ea28 R12: dffffc0000000000
R13: 0000000000000000 R14: 0000000000000010 R15: ffff88811c275100
FS:  0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff75f140000 CR3: 000000010eff6000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ext4_split_extent+0x386/0x4e0 fs/ext4/extents.c:3385
 ext4_split_convert_extents fs/ext4/extents.c:3715 [inline]
 ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3876 [inline]
 ext4_ext_map_blocks+0x1083/0x6080 fs/ext4/extents.c:4231
 ext4_map_blocks+0x9cb/0x1b60 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+0x1260/0x3020 fs/ext4/inode.c:2856
 do_writepages+0x3a9/0x5e0 mm/page-writeback.c:2494
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1622
 writeback_sb_inodes+0x9b8/0x1550 fs/fs-writeback.c:1913
 wb_writeback+0x3f1/0x980 fs/fs-writeback.c:2089
 wb_do_writeback fs/fs-writeback.c:2236 [inline]
 wb_workfn+0x350/0xda0 fs/fs-writeback.c:2276
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_split_extent_at+0xf3f/0xf60 fs/ext4/extents.c:3187
Code: ff ff 44 89 f1 80 e1 07 fe c1 38 c1 0f 8c 45 fb ff ff 4c 89 f7 49 89 f7 e8 fe 5f d0 ff 4c 89 fe e9 32 fb ff ff e8 d1 e7 8b ff <0f> 0b e8 ca e7 8b ff 0f 0b e8 c3 e7 8b ff 0f 0b e8 bc e7 8b ff 0f
RSP: 0018:ffffc90000086ac0 EFLAGS: 00010293
RAX: ffffffff81e4409f RBX: 0000000000000000 RCX: ffff888100298000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000086c30 R08: 0000000000000010 R09: 000000000000043b
R10: ffffed102384ea2a R11: 1ffff1102384ea28 R12: dffffc0000000000
R13: 0000000000000000 R14: 0000000000000010 R15: ffff88811c275100
FS:  0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000010fbd6000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400