==================================================================
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 ffff888139711e18 by task syz.0.2435/9985

CPU: 0 PID: 9985 Comm: syz.0.2435 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2025
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x169/0x1d8 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_split_extent+0x247/0x4e0 fs/ext4/extents.c:3360
 ext4_split_convert_extents fs/ext4/extents.c:3709 [inline]
 ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3870 [inline]
 ext4_ext_map_blocks+0x1b3b/0x5d40 fs/ext4/extents.c:4225
 ext4_map_blocks+0x978/0x1bc0 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+0x11d5/0x2e00 fs/ext4/inode.c:2873
 do_writepages+0x12a/0x270 mm/page-writeback.c:2380
 __filemap_fdatawrite_range+0x2bc/0x360 mm/filemap.c:427
 file_write_and_wait_range+0x8c/0x110 mm/filemap.c:766
 ext4_sync_file+0x1a9/0x9f0 fs/ext4/fsync.c:151
 vfs_fsync_range fs/sync.c:202 [inline]
 vfs_fsync fs/sync.c:216 [inline]
 do_fsync fs/sync.c:226 [inline]
 __do_sys_fdatasync fs/sync.c:240 [inline]
 __se_sys_fdatasync fs/sync.c:238 [inline]
 __x64_sys_fdatasync+0xb8/0x140 fs/sync.c:238
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fd866568ba9
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:00007fd864fb0038 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
RAX: ffffffffffffffda RBX: 00007fd8667b0090 RCX: 00007fd866568ba9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007fd8665ebe19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd8667b0128 R14: 00007fd8667b0090 R15: 00007ffd10f4a178

The buggy address belongs to the page:
page:ffffea0004e5c440 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x139711
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 9954, ts 630066928316, free_ts 631872839259
 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+0x2235/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x268/0x5f0 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+0x1b1/0x300 mm/shmem.c:1584
 shmem_alloc_and_acct_page+0x36f/0x7b0 mm/shmem.c:1609
 shmem_getpage_gfp+0x625/0x2110 mm/shmem.c:1922
 shmem_fault+0x2b7/0x640 mm/shmem.c:2143
 __do_fault mm/memory.c:4064 [inline]
 do_read_fault mm/memory.c:4399 [inline]
 do_fault mm/memory.c:4527 [inline]
 handle_pte_fault+0x1fa5/0x3750 mm/memory.c:4791
 __handle_mm_fault mm/memory.c:4944 [inline]
 handle_mm_fault+0xf3f/0x16a0 mm/memory.c:5358
 faultin_page mm/gup.c:902 [inline]
 __get_user_pages+0xbe9/0x13e0 mm/gup.c:1121
 populate_vma_page_range mm/gup.c:1454 [inline]
 __mm_populate+0x33b/0x420 mm/gup.c:1502
 mm_populate include/linux/mm.h:2793 [inline]
 vm_mmap_pgoff+0x223/0x340 mm/util.c:548
 ksys_mmap_pgoff+0xfd/0x1e0 mm/mmap.c:1712
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:95 [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
 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+0x12e/0x9b0 mm/page_alloc.c:3443
 release_pages+0xe38/0xe80 mm/swap.c:1103
 __pagevec_release+0x71/0xe0 mm/swap.c:1123
 pagevec_release include/linux/pagevec.h:88 [inline]
 shmem_undo_range+0x6e1/0x1760 mm/shmem.c:969
 shmem_truncate_range mm/shmem.c:1073 [inline]
 shmem_evict_inode+0x1fd/0x9c0 mm/shmem.c:1173
 evict+0x478/0x910 fs/inode.c:612
 iput_final fs/inode.c:1736 [inline]
 iput+0x638/0x7c0 fs/inode.c:1762
 dentry_unlink_inode+0x2cf/0x380 fs/dcache.c:378
 __dentry_kill+0x44f/0x650 fs/dcache.c:583
 dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
 dput+0x42/0x80 fs/dcache.c:883
 __fput+0x4fe/0x770 fs/file_table.c:294
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x127/0x190 kernel/task_work.c:189
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xa4f/0x2480 kernel/exit.c:872

Memory state around the buggy address:
 ffff888139711d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888139711d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888139711e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888139711e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888139711f00: 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:3181!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 9985 Comm: syz.0.2435 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2025
RIP: 0010:ext4_split_extent_at+0xe6e/0xe90 fs/ext4/extents.c:3181
Code: 48 89 df 48 89 74 24 68 e8 1f 80 d3 ff 48 8b 74 24 68 e9 5a fb ff ff e8 00 93 99 ff 0f 0b e8 f9 92 99 ff 0f 0b e8 f2 92 99 ff <0f> 0b e8 eb 92 99 ff 0f 0b e8 e4 92 99 ff 0f 0b e8 dd 92 99 ff 0f
RSP: 0018:ffffc90000ec7240 EFLAGS: 00010246
RAX: ffffffff81ca107e RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc9000211e000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90000ec73b0 R08: 0000000000000010 R09: 000000000000043b
R10: fffffbfff0d8ee48 R11: 1ffffffff0d8ee48 R12: 0000000000000010
R13: 0000000000000000 R14: 1ffff110272e7b83 R15: 0000000000000000
FS:  00007fd864fb06c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000d21030 CR3: 0000000120dca000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ext4_split_extent+0x386/0x4e0 fs/ext4/extents.c:3380
 ext4_split_convert_extents fs/ext4/extents.c:3709 [inline]
 ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3870 [inline]
 ext4_ext_map_blocks+0x1b3b/0x5d40 fs/ext4/extents.c:4225
 ext4_map_blocks+0x978/0x1bc0 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+0x11d5/0x2e00 fs/ext4/inode.c:2873
 do_writepages+0x12a/0x270 mm/page-writeback.c:2380
 __filemap_fdatawrite_range+0x2bc/0x360 mm/filemap.c:427
 file_write_and_wait_range+0x8c/0x110 mm/filemap.c:766
 ext4_sync_file+0x1a9/0x9f0 fs/ext4/fsync.c:151
 vfs_fsync_range fs/sync.c:202 [inline]
 vfs_fsync fs/sync.c:216 [inline]
 do_fsync fs/sync.c:226 [inline]
 __do_sys_fdatasync fs/sync.c:240 [inline]
 __se_sys_fdatasync fs/sync.c:238 [inline]
 __x64_sys_fdatasync+0xb8/0x140 fs/sync.c:238
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fd866568ba9
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:00007fd864fb0038 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
RAX: ffffffffffffffda RBX: 00007fd8667b0090 RCX: 00007fd866568ba9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007fd8665ebe19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd8667b0128 R14: 00007fd8667b0090 R15: 00007ffd10f4a178
Modules linked in:
---[ end trace c17304f2b5c4fc10 ]---
RIP: 0010:ext4_split_extent_at+0xe6e/0xe90 fs/ext4/extents.c:3181
Code: 48 89 df 48 89 74 24 68 e8 1f 80 d3 ff 48 8b 74 24 68 e9 5a fb ff ff e8 00 93 99 ff 0f 0b e8 f9 92 99 ff 0f 0b e8 f2 92 99 ff <0f> 0b e8 eb 92 99 ff 0f 0b e8 e4 92 99 ff 0f 0b e8 dd 92 99 ff 0f
RSP: 0018:ffffc90000ec7240 EFLAGS: 00010246
RAX: ffffffff81ca107e RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc9000211e000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90000ec73b0 R08: 0000000000000010 R09: 000000000000043b
R10: fffffbfff0d8ee48 R11: 1ffffffff0d8ee48 R12: 0000000000000010
R13: 0000000000000000 R14: 1ffff110272e7b83 R15: 0000000000000000
FS:  00007fd864fb06c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2dff4ff8 CR3: 0000000120dca000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400