sysv_free_block: flc_count > flc_size
sysv_free_block: flc_count > flc_size
sysv_free_block: flc_count > flc_size
==================================================================
BUG: KASAN: use-after-free in sysv_new_block+0x73f/0x910 fs/sysv/balloc.c:113
Read of size 4 at addr ffff8880812f60c8 by task syz-executor.4/10323

CPU: 0 PID: 10323 Comm: syz-executor.4 Not tainted 6.2.0-rc5-syzkaller-00047-g7c46948a6e9c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/12/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x290 lib/dump_stack.c:106
 print_address_description+0x74/0x340 mm/kasan/report.c:306
 print_report+0x107/0x1f0 mm/kasan/report.c:417
 kasan_report+0xcd/0x100 mm/kasan/report.c:517
 sysv_new_block+0x73f/0x910 fs/sysv/balloc.c:113
 alloc_branch fs/sysv/itree.c:134 [inline]
 get_block+0x2b5/0x16d0 fs/sysv/itree.c:251
 __block_write_begin_int+0x54c/0x1a80 fs/buffer.c:1991
 __block_write_begin fs/buffer.c:2041 [inline]
 block_write_begin+0x93/0x1e0 fs/buffer.c:2102
 sysv_write_begin+0x2d/0x60 fs/sysv/itree.c:485
 generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
 __generic_file_write_iter+0x176/0x400 mm/filemap.c:3900
 generic_file_write_iter+0xab/0x310 mm/filemap.c:3932
 call_write_iter include/linux/fs.h:2189 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x7dc/0xc50 fs/read_write.c:584
 ksys_write+0x177/0x2a0 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f8f2828c0c9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8f29085168 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f8f283abf80 RCX: 00007f8f2828c0c9
RDX: 000000000000087a RSI: 000000002000a100 RDI: 0000000000000004
RBP: 00007f8f282e7ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fffcc8426bf R14: 00007f8f29085300 R15: 0000000000022000
 </TASK>

The buggy address belongs to the physical page:
page:ffffea000204bd80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x812f6
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000001 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 8054, tgid 8053 (syz-executor.5), ts 274280408394, free_ts 275833106644
 prep_new_page mm/page_alloc.c:2531 [inline]
 get_page_from_freelist+0x742/0x7c0 mm/page_alloc.c:4283
 __alloc_pages+0x259/0x560 mm/page_alloc.c:5549
 __folio_alloc+0xf/0x30 mm/page_alloc.c:5581
 vma_alloc_folio+0x660/0xb60 mm/mempolicy.c:2247
 shmem_alloc_folio mm/shmem.c:1569 [inline]
 shmem_alloc_and_acct_folio+0x594/0xd70 mm/shmem.c:1593
 shmem_get_folio_gfp+0x1751/0x3a30 mm/shmem.c:1920
 shmem_get_folio mm/shmem.c:2051 [inline]
 shmem_write_begin+0x133/0x480 mm/shmem.c:2543
 generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
 __generic_file_write_iter+0x176/0x400 mm/filemap.c:3900
 generic_file_write_iter+0xab/0x310 mm/filemap.c:3932
 call_write_iter include/linux/fs.h:2189 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x7dc/0xc50 fs/read_write.c:584
 ksys_write+0x177/0x2a0 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1446 [inline]
 free_pcp_prepare+0x751/0x780 mm/page_alloc.c:1496
 free_unref_page_prepare mm/page_alloc.c:3369 [inline]
 free_unref_page_list+0xb2/0x830 mm/page_alloc.c:3510
 release_pages+0x233e/0x25e0 mm/swap.c:1076
 __pagevec_release+0x7d/0xf0 mm/swap.c:1096
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x6d0/0x1fe0 mm/shmem.c:947
 shmem_truncate_range mm/shmem.c:1042 [inline]
 shmem_evict_inode+0x276/0xa10 mm/shmem.c:1151
 evict+0x2a4/0x620 fs/inode.c:664
 __dentry_kill+0x3b1/0x5b0 fs/dcache.c:607
 dentry_kill+0xbb/0x290
 dput+0x1f3/0x410 fs/dcache.c:913
 __fput+0x5e4/0x880 fs/file_table.c:328
 task_work_run+0x243/0x300 kernel/task_work.c:179
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0x124/0x150 kernel/entry/common.c:171
 exit_to_user_mode_prepare+0xb2/0x140 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x26/0x60 kernel/entry/common.c:296
 do_syscall_64+0x49/0xb0 arch/x86/entry/common.c:86

Memory state around the buggy address:
 ffff8880812f5f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880812f6000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880812f6080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff8880812f6100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880812f6180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================