==================================================================
BUG: KASAN: use-after-free in leaf_paste_in_buffer+0x1c8/0xa14 fs/reiserfs/lbalance.c:1017
Write of size 4096 at addr ffff0000f6c9fe8c by task syz.7.244/6138

CPU: 1 PID: 6138 Comm: syz.7.244 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
 dump_backtrace+0x1c0/0x1ec arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 print_address_description+0x88/0x218 mm/kasan/report.c:316
 print_report+0x50/0x68 mm/kasan/report.c:420
 kasan_report+0xa8/0xfc mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x258/0x290 mm/kasan/generic.c:189
 memmove+0x60/0x90 mm/kasan/shadow.c:55
 leaf_paste_in_buffer+0x1c8/0xa14 fs/reiserfs/lbalance.c:1017
 leaf_copy_boundary_item+0x930/0x19dc fs/reiserfs/lbalance.c:199
 leaf_copy_items fs/reiserfs/lbalance.c:551 [inline]
 leaf_move_items+0x6a0/0xbb0 fs/reiserfs/lbalance.c:726
 leaf_shift_left+0xc8/0x3ac fs/reiserfs/lbalance.c:750
 balance_leaf_paste_left_shift fs/reiserfs/do_balan.c:458 [inline]
 balance_leaf_paste_left fs/reiserfs/do_balan.c:592 [inline]
 balance_leaf_left fs/reiserfs/do_balan.c:613 [inline]
 balance_leaf+0x84e0/0xd92c fs/reiserfs/do_balan.c:1409
 do_balance+0x270/0x790 fs/reiserfs/do_balan.c:1888
 reiserfs_paste_into_item+0x5d0/0x6e0 fs/reiserfs/stree.c:2159
 reiserfs_get_block+0x14a0/0x36e8 fs/reiserfs/inode.c:1069
 __block_write_begin_int+0x350/0x1388 fs/buffer.c:1991
 __block_write_begin+0x7c/0xa0 fs/buffer.c:2041
 reiserfs_write_begin+0x328/0x714 fs/reiserfs/inode.c:2775
 generic_perform_write+0x234/0x4f4 mm/filemap.c:3862
 __generic_file_write_iter+0x130/0x250 mm/filemap.c:3960
 generic_file_write_iter+0xb4/0x2b0 mm/filemap.c:3989
 do_iter_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x53c/0x940 fs/read_write.c:861
 vfs_writev fs/read_write.c:934 [inline]
 do_pwritev+0x1e8/0x338 fs/read_write.c:1031
 __do_sys_pwritev2 fs/read_write.c:1090 [inline]
 __se_sys_pwritev2 fs/read_write.c:1081 [inline]
 __arm64_sys_pwritev2+0xd4/0x108 fs/read_write.c:1081
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

The buggy address belongs to the physical page:
page:000000009a3ab950 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x136c9f
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000f6c9fd80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f6c9fe00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff0000f6c9fe80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff0000f6c9ff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f6c9ff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
REISERFS warning: reiserfs-5090 is_tree_node: node level 0 does not match to the expected one 2
REISERFS error (device loop7): vs-5150 search_by_key: invalid format found in block 531. Fsck?
REISERFS (device loop7): Remounting filesystem read-only
REISERFS warning: reiserfs-5090 is_tree_node: node level 0 does not match to the expected one 2
REISERFS error (device loop7): vs-5150 search_by_key: invalid format found in block 531. Fsck?
REISERFS error (device loop7): clm-6001 reiserfs_truncate_file: grab_tail_page failed -5