==================================================================
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 ffff88813e40b8e8 by task syz.3.2285/7909

CPU: 1 PID: 7909 Comm: syz.3.2285 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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_remove_space+0x2f0/0x4570 fs/ext4/extents.c:2829
 ext4_punch_hole+0x6f8/0xad0 fs/ext4/inode.c:4223
 ext4_fallocate+0x271/0x1a70 fs/ext4/extents.c:4758
 vfs_fallocate+0x4b4/0x590 fs/open.c:310
 madvise_remove mm/madvise.c:880 [inline]
 madvise_vma_behavior mm/madvise.c:904 [inline]
 madvise_walk_vmas mm/madvise.c:1131 [inline]
 do_madvise+0x1443/0x1d70 mm/madvise.c:1308
 __do_sys_madvise mm/madvise.c:1322 [inline]
 __se_sys_madvise mm/madvise.c:1320 [inline]
 __x64_sys_madvise+0xa9/0xc0 mm/madvise.c:1320
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f907a86af79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f90792a5028 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f907aae5090 RCX: 00007f907a86af79
RDX: 0000000000000009 RSI: 0000000000600002 RDI: 0000200000000000
RBP: 00007f907a9017e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f907aae5128 R14: 00007f907aae5090 R15: 00007ffd3fb31f08

The buggy address belongs to the page:
page:ffffea0004f902c0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x13e40b
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 7693, ts 302449159155, free_ts 303379503560
 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_fallocate+0x841/0xc40 mm/shmem.c:2824
 vfs_fallocate+0x4b4/0x590 fs/open.c:310
 ksys_fallocate fs/open.c:333 [inline]
 __do_sys_fallocate fs/open.c:341 [inline]
 __se_sys_fallocate fs/open.c:339 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:339
 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:
 ffff88813e40b780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88813e40b800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88813e40b880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                          ^
 ffff88813e40b900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88813e40b980: 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: 0 PID: 7909 Comm: syz.3.2285 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:ext4_split_extent_at+0xe65/0xe90 fs/ext4/extents.c:3181
Code: 71 cf d2 ff e9 f1 fb ff ff 89 d9 80 e1 07 fe c1 38 c1 0f 8c fe fb ff ff 48 89 df e8 35 cf d2 ff e9 f1 fb ff ff e8 5b 4e 98 ff <0f> 0b e8 54 4e 98 ff 0f 0b e8 4d 4e 98 ff 0f 0b e8 46 4e 98 ff 0f
RSP: 0018:ffffc90000bf74a0 EFLAGS: 00010283
RAX: ffffffff81cc67f5 RBX: 1ffff11027c867b7 RCX: 0000000000080000
RDX: ffffc90004948000 RSI: 0000000000056ffd RDI: 0000000000056ffe
RBP: ffffc90000bf7610 R08: 0000000000000000 R09: 0000000050000028
R10: dffffc0000000000 R11: fffffbfff0dcf448 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f90792a56c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f20cd54c000 CR3: 0000000112e2f000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ext4_force_split_extent_at fs/ext4/extents.c:318 [inline]
 ext4_ext_remove_space+0x631/0x4570 fs/ext4/extents.c:2875
 ext4_punch_hole+0x6f8/0xad0 fs/ext4/inode.c:4223
 ext4_fallocate+0x271/0x1a70 fs/ext4/extents.c:4758
 vfs_fallocate+0x4b4/0x590 fs/open.c:310
 madvise_remove mm/madvise.c:880 [inline]
 madvise_vma_behavior mm/madvise.c:904 [inline]
 madvise_walk_vmas mm/madvise.c:1131 [inline]
 do_madvise+0x1443/0x1d70 mm/madvise.c:1308
 __do_sys_madvise mm/madvise.c:1322 [inline]
 __se_sys_madvise mm/madvise.c:1320 [inline]
 __x64_sys_madvise+0xa9/0xc0 mm/madvise.c:1320
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f907a86af79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f90792a5028 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f907aae5090 RCX: 00007f907a86af79
RDX: 0000000000000009 RSI: 0000000000600002 RDI: 0000200000000000
RBP: 00007f907a9017e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f907aae5128 R14: 00007f907aae5090 R15: 00007ffd3fb31f08
Modules linked in:
---[ end trace 6425a2a43314daa2 ]---
RIP: 0010:ext4_split_extent_at+0xe65/0xe90 fs/ext4/extents.c:3181
Code: 71 cf d2 ff e9 f1 fb ff ff 89 d9 80 e1 07 fe c1 38 c1 0f 8c fe fb ff ff 48 89 df e8 35 cf d2 ff e9 f1 fb ff ff e8 5b 4e 98 ff <0f> 0b e8 54 4e 98 ff 0f 0b e8 4d 4e 98 ff 0f 0b e8 46 4e 98 ff 0f
RSP: 0018:ffffc90000bf74a0 EFLAGS: 00010283
RAX: ffffffff81cc67f5 RBX: 1ffff11027c867b7 RCX: 0000000000080000
RDX: ffffc90004948000 RSI: 0000000000056ffd RDI: 0000000000056ffe
RBP: ffffc90000bf7610 R08: 0000000000000000 R09: 0000000050000028
R10: dffffc0000000000 R11: fffffbfff0dcf448 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f90792a56c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9cc4eec198 CR3: 0000000112e2f000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400