==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:827 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:946
Read of size 4 at addr ffff88812f8fe018 by task syz.0.12/382

CPU: 0 PID: 382 Comm: syz.0.12 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0xf1/0x140 mm/kasan/report.c:444
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ext4_ext_binsearch fs/ext4/extents.c:827 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:946
 ext4_ext_map_blocks+0x1de/0x6280 fs/ext4/extents.c:4166
 ext4_map_blocks+0x97b/0x1b20 fs/ext4/inode.c:674
 mpage_map_one_extent fs/ext4/inode.c:2421 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2474 [inline]
 ext4_writepages+0x11e7/0x2f90 fs/ext4/inode.c:2842
 do_writepages+0x48a/0x6c0 mm/page-writeback.c:2388
 filemap_fdatawrite_wbc+0x1f4/0x250 mm/filemap.c:409
 __filemap_fdatawrite_range mm/filemap.c:442 [inline]
 filemap_write_and_wait_range+0xfa/0x380 mm/filemap.c:713
 ext4_punch_hole+0x120/0xbd0 fs/ext4/inode.c:4026
 ext4_fallocate+0x2b6/0x1de0 fs/ext4/extents.c:4765
 vfs_fallocate+0x4b4/0x590 fs/open.c:309
 madvise_remove mm/madvise.c:964 [inline]
 madvise_vma_behavior mm/madvise.c:988 [inline]
 madvise_walk_vmas mm/madvise.c:1218 [inline]
 do_madvise+0x12c8/0x2200 mm/madvise.c:1396
 __do_sys_madvise mm/madvise.c:1409 [inline]
 __se_sys_madvise mm/madvise.c:1407 [inline]
 __x64_sys_madvise+0xa9/0xc0 mm/madvise.c:1407
 x64_sys_call+0x89b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:29
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f6fa2cc8ec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6fa1731038 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f6fa2f1ffa0 RCX: 00007f6fa2cc8ec9
RDX: 0000000000000009 RSI: 0000000000600003 RDI: 0000200000000000
RBP: 00007f6fa2d4bf91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6fa2f20038 R14: 00007f6fa2f1ffa0 R15: 00007ffe52d5df08
 </TASK>

The buggy address belongs to the page:
page:ffffea0004be3f80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12f8fe
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004be3fc8 ffffea0004be37c8 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 397, ts 29735704363, free_ts 29784937031
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
 get_page_from_freelist+0x2cc5/0x2d50 mm/page_alloc.c:4485
 __alloc_pages+0x18f/0x440 mm/page_alloc.c:5808
 __alloc_pages_node include/linux/gfp.h:595 [inline]
 alloc_pages_node include/linux/gfp.h:609 [inline]
 alloc_pages include/linux/gfp.h:622 [inline]
 shmem_alloc_page mm/shmem.c:1591 [inline]
 shmem_alloc_and_acct_page+0x42b/0x870 mm/shmem.c:1616
 shmem_getpage_gfp+0xfe5/0x2310 mm/shmem.c:1912
 shmem_getpage mm/shmem.c:156 [inline]
 shmem_write_begin+0xce/0x1b0 mm/shmem.c:2480
 generic_perform_write+0x2ad/0x670 mm/filemap.c:3870
 __generic_file_write_iter+0x268/0x480 mm/filemap.c:3998
 generic_file_write_iter+0xa9/0x1d0 mm/filemap.c:4030
 call_write_iter include/linux/fs.h:2212 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x802/0xf70 fs/read_write.c:594
 ksys_write+0x140/0x240 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:656
 x64_sys_call+0x8ef/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1472 [inline]
 free_pcp_prepare mm/page_alloc.c:1544 [inline]
 free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
 free_unref_page_list+0x134/0x9d0 mm/page_alloc.c:3671
 release_pages+0xfda/0x1030 mm/swap.c:1014
 __pagevec_release+0x71/0xe0 mm/swap.c:1034
 pagevec_release include/linux/pagevec.h:81 [inline]
 shmem_undo_range+0x53f/0x13d0 mm/shmem.c:969
 shmem_truncate_range mm/shmem.c:1068 [inline]
 shmem_evict_inode+0x1fd/0x9c0 mm/shmem.c:1150
 evict+0x485/0x870 fs/inode.c:650
 iput_final fs/inode.c:1779 [inline]
 iput+0x635/0x7c0 fs/inode.c:1805
 dentry_unlink_inode+0x32f/0x3e0 fs/dcache.c:380
 __dentry_kill+0x44f/0x650 fs/dcache.c:586
 dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
 dput+0x47/0x90 fs/dcache.c:893
 __fput+0x580/0x8b0 fs/file_table.c:319
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181

Memory state around the buggy address:
 ffff88812f8fdf00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812f8fdf80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812f8fe000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88812f8fe080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812f8fe100: 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:3186!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 382 Comm: syz.0.12 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:ext4_split_extent_at+0xe77/0xe90 fs/ext4/extents.c:3186
Code: 6f fb ff ff 48 89 df 49 89 d7 e8 b4 79 d3 ff 4c 89 fa e9 5c fb ff ff e8 f7 fa 94 ff 0f 0b e8 f0 fa 94 ff 0f 0b e8 e9 fa 94 ff <0f> 0b e8 e2 fa 94 ff 0f 0b e8 db fa 94 ff 0f 0b e8 d4 fa 94 ff 0f
RSP: 0018:ffffc90000af74e0 EFLAGS: 00010246
RAX: ffffffff81d3c3c7 RBX: 1ffff11025f2ab83 RCX: 0000000000080000
RDX: ffffc900012eb000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90000af7650 R08: 0000000000000000 R09: 0000000050000028
R10: ffffed10252f2aaa R11: 1ffff110252f2aa8 R12: dffffc0000000000
R13: 00000000000000c8 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f6fa17316c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4aa64f2ad8 CR3: 000000010ddc6000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ext4_force_split_extent_at fs/ext4/extents.c:319 [inline]
 ext4_ext_remove_space+0x64b/0x4180 fs/ext4/extents.c:2880
 ext4_punch_hole+0x77c/0xbd0 fs/ext4/inode.c:4131
 ext4_fallocate+0x2b6/0x1de0 fs/ext4/extents.c:4765
 vfs_fallocate+0x4b4/0x590 fs/open.c:309
 madvise_remove mm/madvise.c:964 [inline]
 madvise_vma_behavior mm/madvise.c:988 [inline]
 madvise_walk_vmas mm/madvise.c:1218 [inline]
 do_madvise+0x12c8/0x2200 mm/madvise.c:1396
 __do_sys_madvise mm/madvise.c:1409 [inline]
 __se_sys_madvise mm/madvise.c:1407 [inline]
 __x64_sys_madvise+0xa9/0xc0 mm/madvise.c:1407
 x64_sys_call+0x89b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:29
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f6fa2cc8ec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6fa1731038 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f6fa2f1ffa0 RCX: 00007f6fa2cc8ec9
RDX: 0000000000000009 RSI: 0000000000600003 RDI: 0000200000000000
RBP: 00007f6fa2d4bf91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6fa2f20038 R14: 00007f6fa2f1ffa0 R15: 00007ffe52d5df08
 </TASK>
Modules linked in:
---[ end trace c8ef0b6e7a0738c0 ]---
RIP: 0010:ext4_split_extent_at+0xe77/0xe90 fs/ext4/extents.c:3186
Code: 6f fb ff ff 48 89 df 49 89 d7 e8 b4 79 d3 ff 4c 89 fa e9 5c fb ff ff e8 f7 fa 94 ff 0f 0b e8 f0 fa 94 ff 0f 0b e8 e9 fa 94 ff <0f> 0b e8 e2 fa 94 ff 0f 0b e8 db fa 94 ff 0f 0b e8 d4 fa 94 ff 0f
RSP: 0018:ffffc90000af74e0 EFLAGS: 00010246
RAX: ffffffff81d3c3c7 RBX: 1ffff11025f2ab83 RCX: 0000000000080000
RDX: ffffc900012eb000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90000af7650 R08: 0000000000000000 R09: 0000000050000028
R10: ffffed10252f2aaa R11: 1ffff110252f2aa8 R12: dffffc0000000000
R13: 00000000000000c8 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f6fa17316c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbd5ecac130 CR3: 000000010ddc6000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400