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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 ffff0000f2a550c8 by task syz.2.76/7052

CPU: 0 UID: 0 PID: 7052 Comm: syz.2.76 Not tainted 6.14.0-rc7-syzkaller-ga2392f333575 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xe4/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x198/0x550 mm/kasan/report.c:521
 kasan_report+0xd8/0x138 mm/kasan/report.c:634
 __asan_report_load4_noabort+0x20/0x2c mm/kasan/report_generic.c:380
 sysv_new_block+0x618/0x7e4 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:135 [inline]
 get_block+0x254/0x1350 fs/sysv/itree.c:254
 __block_write_begin_int+0x4c4/0x1610 fs/buffer.c:2116
 block_write_begin+0xa0/0x11c fs/buffer.c:2226
 sysv_write_begin+0x44/0x88 fs/sysv/itree.c:490
 page_symlink+0x268/0x928 fs/namei.c:5436
 sysv_symlink+0xd4/0x174 fs/sysv/namei.c:86
 vfs_symlink+0x138/0x28c fs/namei.c:4671
 do_symlinkat+0x1c4/0x46c fs/namei.c:4697
 __do_sys_symlinkat fs/namei.c:4713 [inline]
 __se_sys_symlinkat fs/namei.c:4710 [inline]
 __arm64_sys_symlinkat+0x9c/0xb4 fs/namei.c:4710
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x322 pfn:0x132a55
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000322 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000f2a54f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f2a55000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff0000f2a55080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff0000f2a55100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000f2a55180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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