loop0: detected capacity change from 0 to 128
VFS: Found a Xenix FS (block size = 1024) on device loop0
unable to read i-node block
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BUG: KASAN: use-after-free in sysv_new_block+0x790/0x970 fs/sysv/balloc.c:113
Read of size 4 at addr ffff88804d8960c8 by task syz.0.0/5321

CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted 6.14.0-rc7-syzkaller-00137-g5fc319360819 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x16e/0x5b0 mm/kasan/report.c:521
 kasan_report+0x143/0x180 mm/kasan/report.c:634
 sysv_new_block+0x790/0x970 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:135 [inline]
 get_block+0x30a/0x16e0 fs/sysv/itree.c:254
 __block_write_begin_int+0x692/0x19a0 fs/buffer.c:2116
 sysv_make_empty+0xa8/0x640 fs/sysv/dir.c:262
 sysv_mkdir+0x7f/0x130 fs/sysv/namei.c:130
 vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4313
 do_mkdirat+0x264/0x3a0 fs/namei.c:4336
 __do_sys_mkdirat fs/namei.c:4351 [inline]
 __se_sys_mkdirat fs/namei.c:4349 [inline]
 __x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4349
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa99d38d169
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:00007fa99e27d038 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007fa99d5a5fa0 RCX: 00007fa99d38d169
RDX: 0000000000000000 RSI: 0000200000002040 RDI: ffffffffffffff9c
RBP: 00007fa99d40e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fa99d5a5fa0 R15: 00007ffff00931a8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4d896
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea00013625c8 ffffea0001362548 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff88804d895f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804d896000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804d896080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff88804d896100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804d896180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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