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BUG: KASAN: use-after-free in sysv_new_block+0x618/0x7e4 fs/sysv/balloc.c:113
Read of size 4 at addr ffff0000f69630c8 by task syz.4.195/5347

CPU: 1 PID: 5347 Comm: syz.4.195 Not tainted 6.1.131-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0x174/0x4c0 mm/kasan/report.c:427
 kasan_report+0xd4/0x130 mm/kasan/report.c:531
 __asan_report_load4_noabort+0x2c/0x38 mm/kasan/report_generic.c:350
 sysv_new_block+0x618/0x7e4 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:134 [inline]
 get_block+0x254/0x1360 fs/sysv/itree.c:253
 __block_write_begin_int+0x340/0x13b4 fs/buffer.c:1991
 __block_write_begin+0x7c/0xa0 fs/buffer.c:2041
 sysv_prepare_chunk+0x3c/0x50 fs/sysv/itree.c:468
 sysv_make_empty+0x98/0x500 fs/sysv/dir.c:257
 sysv_mkdir+0x88/0x138 fs/sysv/namei.c:130
 vfs_mkdir+0x334/0x4e4 fs/namei.c:4106
 do_mkdirat+0x220/0x510 fs/namei.c:4131
 __do_sys_mkdirat fs/namei.c:4146 [inline]
 __se_sys_mkdirat fs/namei.c:4144 [inline]
 __arm64_sys_mkdirat+0x90/0xa8 fs/namei.c:4144
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x168 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:0000000084e1130e refcount:1 mapcount:0 mapping:000000008a726ae5 index:0x12a pfn:0x136963
memcg:ffff0000dc1a2000
aops:shmem_aops ino:5f dentry name(?):"memfd:syzkaller"
flags: 0x5ffd8000008001e(referenced|uptodate|dirty|lru|swapbacked|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffd8000008001e fffffc0003da5888 fffffc0003e47b08 ffff0000f9d45bc8
raw: 000000000000012a 0000000000000000 00000001ffffffff ffff0000dc1a2000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000f6962f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff0000f6963000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff0000f6963080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                                              ^
 ffff0000f6963100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff0000f6963180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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