loop4: detected capacity change from 0 to 128
VFS: Found a Xenix FS (block size = 1024) on device loop4
Buffer I/O error on dev loop4, logical block 3245768, async page read
==================================================================
BUG: KASAN: use-after-free in sysv_new_block+0x7a7/0xa50 fs/sysv/balloc.c:113
Read of size 4 at addr ffff88805232b0c8 by task syz.4.41/6143

CPU: 1 UID: 0 PID: 6143 Comm: syz.4.41 Not tainted 6.12.0-syzkaller-10296-gaaf20f870da0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xc3/0x620 mm/kasan/report.c:489
 kasan_report+0xd9/0x110 mm/kasan/report.c:602
 sysv_new_block+0x7a7/0xa50 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:135 [inline]
 get_block+0x261/0x1570 fs/sysv/itree.c:254
 __block_write_begin_int+0x4fe/0x16e0 fs/buffer.c:2116
 block_write_begin+0x9a/0x1d0 fs/buffer.c:2226
 sysv_write_begin+0x31/0xe0 fs/sysv/itree.c:490
 page_symlink+0x3bc/0x440 fs/namei.c:5416
 sysv_symlink+0xd3/0x180 fs/sysv/namei.c:86
 vfs_symlink fs/namei.c:4669 [inline]
 vfs_symlink+0x3eb/0x660 fs/namei.c:4653
 do_symlinkat+0x263/0x310 fs/namei.c:4695
 __do_sys_symlink fs/namei.c:4716 [inline]
 __se_sys_symlink fs/namei.c:4714 [inline]
 __x64_sys_symlink+0x75/0x90 fs/namei.c:4714
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f790f380809
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:00007f790d1f6058 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007f790f545fa0 RCX: 00007f790f380809
RDX: 0000000000000000 RSI: 0000000020000200 RDI: 00000000200049c0
RBP: 00007f790f3f393e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f790f545fa0 R15: 00007ffead1a0218
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x2732 pfn:0x5232b
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000002732 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 6015, tgid 6013 (syz.1.17), ts 104862564977, free_ts 110062846741
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1556
 prep_new_page mm/page_alloc.c:1564 [inline]
 get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3474
 __alloc_pages_noprof+0x223/0x25a0 mm/page_alloc.c:4751
 alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2265
 folio_alloc_mpol_noprof+0x36/0xd0 mm/mempolicy.c:2283
 shmem_alloc_folio+0x135/0x160 mm/shmem.c:1794
 shmem_alloc_and_add_folio+0x48b/0xc00 mm/shmem.c:1833
 shmem_get_folio_gfp+0x689/0x1530 mm/shmem.c:2355
 shmem_get_folio mm/shmem.c:2461 [inline]
 shmem_write_begin+0x161/0x300 mm/shmem.c:3117
 generic_perform_write+0x2bd/0x920 mm/filemap.c:4055
 shmem_file_write_iter+0x10e/0x140 mm/shmem.c:3293
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5b1/0x1150 fs/read_write.c:679
 ksys_write+0x12b/0x250 fs/read_write.c:731
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5863 tgid 5863 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_unref_folios+0xa7b/0x14f0 mm/page_alloc.c:2704
 folios_put_refs+0x587/0x7b0 mm/swap.c:962
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x586/0x1170 mm/shmem.c:1040
 shmem_truncate_range mm/shmem.c:1152 [inline]
 shmem_evict_inode+0x3a3/0xba0 mm/shmem.c:1280
 evict+0x40c/0x960 fs/inode.c:796
 iput_final fs/inode.c:1946 [inline]
 iput fs/inode.c:1972 [inline]
 iput+0x52a/0x890 fs/inode.c:1958
 dentry_unlink_inode+0x29c/0x480 fs/dcache.c:422
 __dentry_kill+0x1d0/0x600 fs/dcache.c:625
 dput.part.0+0x4b1/0x9b0 fs/dcache.c:867
 dput+0x1f/0x30 fs/dcache.c:857
 __fput+0x515/0xb60 fs/file_table.c:458
 task_work_run+0x151/0x250 kernel/task_work.c:239
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88805232af80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805232b000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88805232b080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff88805232b100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805232b180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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