VFS: Found a Xenix FS (block size = 1024) on device loop0
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5023 at fs/inode.c:389 inc_nlink+0x128/0x150 fs/inode.c:389
Modules linked in:
CPU: 0 PID: 5023 Comm: syz.0.125 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : inc_nlink+0x128/0x150 fs/inode.c:389
lr : inc_nlink+0x128/0x150 fs/inode.c:389
sp : ffff800021437b90
x29: ffff800021437b90 x28: dfff800000000000 x27: 0000000000000000
x26: 1fffe0001c3d880c x25: ffff800011e15848 x24: 00000000000001c0
x23: 1fffe0001c3d8810 x22: dfff800000000000 x21: 0000000000000000
x20: ffff0000e1ec4038 x19: ffff0000e1ec4080 x18: 0000000000000000
x17: ffff800018349000 x16: ffff8000082d9364 x15: 0000000000000000
x14: 0000000000000001 x13: 1fffe00018108856 x12: 0000000000080000
x11: 000000000000358c x10: ffff800021dbb000 x9 : ffff800008a0c460
x8 : 000000000000358d x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 000000000000000c x3 : 00000000000001c0
x2 : ffff0000e1f022f0 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
 inc_nlink+0x128/0x150 fs/inode.c:389
 inode_inc_link_count include/linux/fs.h:2576 [inline]
 sysv_mkdir+0x2c/0x138 fs/sysv/namei.c:119
 vfs_mkdir+0x314/0x4d4 fs/namei.c:4114
 do_mkdirat+0x1b8/0x3ec fs/namei.c:4139
 __do_sys_mkdirat fs/namei.c:4154 [inline]
 __se_sys_mkdirat fs/namei.c:4152 [inline]
 __arm64_sys_mkdirat+0x90/0xa8 fs/namei.c:4152
 __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
irq event stamp: 5432
hardirqs last  enabled at (5431): [<ffff8000088e6578>] kasan_quarantine_put+0xc4/0x200 mm/kasan/quarantine.c:242
hardirqs last disabled at (5432): [<ffff800011a223fc>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:405
softirqs last  enabled at (5410): [<ffff800008030954>] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32
softirqs last disabled at (5408): [<ffff800008030920>] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19
---[ end trace 0000000000000000 ]---
==================================================================
BUG: KASAN: use-after-free in sysv_new_inode+0xda8/0xf20 fs/sysv/ialloc.c:153
Read of size 2 at addr ffff0000e47001ce by task syz.0.125/5023

CPU: 1 PID: 5023 Comm: syz.0.125 Tainted: G        W          syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
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
 __asan_report_load2_noabort+0x2c/0x38 mm/kasan/report_generic.c:349
 sysv_new_inode+0xda8/0xf20 fs/sysv/ialloc.c:153
 sysv_mkdir+0x44/0x138 fs/sysv/namei.c:121
 vfs_mkdir+0x314/0x4d4 fs/namei.c:4114
 do_mkdirat+0x1b8/0x3ec fs/namei.c:4139
 __do_sys_mkdirat fs/namei.c:4154 [inline]
 __se_sys_mkdirat fs/namei.c:4152 [inline]
 __arm64_sys_mkdirat+0x90/0xa8 fs/namei.c:4152
 __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:000000002ea172b1 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x1 pfn:0x124700
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffc0003ece008 fffffc0003ea0008 0000000000000000
raw: 0000000000000001 0000000000000007 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000e4700080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000e4700100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff0000e4700180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff0000e4700200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000e4700280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
syz.0.125: attempt to access beyond end of device
loop0: rw=2049, sector=6491536, nr_sectors = 2 limit=128
Buffer I/O error on dev loop0, logical block 3245768, lost async page write
UBIFS error (pid: 5023): cannot open "/dev/nbd0", error -22