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BUG: KASAN: use-after-free in sysv_new_block+0x5d0/0x768 fs/sysv/balloc.c:113
Read of size 4 at addr ffff0000f77480c8 by task syz.4.5/4493

CPU: 1 PID: 4493 Comm: syz.4.5 Not tainted 6.1.147-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/18/2025
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106
 print_address_description+0x88/0x200 mm/kasan/report.c:316
 print_report+0x50/0x68 mm/kasan/report.c:418
 kasan_report+0xa8/0x100 mm/kasan/report.c:522
 __asan_report_load4_noabort+0x2c/0x38 mm/kasan/report_generic.c:350
 sysv_new_block+0x5d0/0x768 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:134 [inline]
 get_block+0x204/0x1210 fs/sysv/itree.c:253
 __block_write_begin_int+0x34c/0x13b8 fs/buffer.c:1991
 __block_write_begin fs/buffer.c:2041 [inline]
 block_write_begin+0x98/0x11c fs/buffer.c:2102
 sysv_write_begin+0x44/0x88 fs/sysv/itree.c:487
 generic_perform_write+0x230/0x4b0 mm/filemap.c:3846
 __generic_file_write_iter+0x168/0x37c mm/filemap.c:3974
 generic_file_write_iter+0xb4/0x2b0 mm/filemap.c:4006
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x5ac/0x7c4 fs/read_write.c:584
 ksys_write+0x120/0x210 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:646
 __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+0x58/0x138 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:000000009ed75c0c refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x137748
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffc0003ddd248 fffffc0003ddd1c8 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000f7747f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f7748000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff0000f7748080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff0000f7748100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f7748180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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