==================================================================
BUG: KASAN: use-after-free in sysv_new_block+0x7a7/0xa50 fs/sysv/balloc.c:113
Read of size 4 at addr ffff8880663b70c8 by task syz-executor.1/6782

CPU: 2 PID: 6782 Comm: syz-executor.1 Not tainted 6.10.0-rc2-syzkaller-00235-g8a92980606e3 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0xc3/0x620 mm/kasan/report.c:488
 kasan_report+0xd9/0x110 mm/kasan/report.c:601
 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+0x4fb/0x16e0 fs/buffer.c:2128
 __block_write_begin fs/buffer.c:2177 [inline]
 block_write_begin+0xb1/0x4a0 fs/buffer.c:2236
 sysv_write_begin+0x31/0xe0 fs/sysv/itree.c:490
 page_symlink+0x3b9/0x440 fs/namei.c:5236
 sysv_symlink+0xd3/0x180 fs/sysv/namei.c:86
 vfs_symlink fs/namei.c:4489 [inline]
 vfs_symlink+0x3e8/0x660 fs/namei.c:4473
 do_symlinkat+0x263/0x310 fs/namei.c:4515
 __do_sys_symlink fs/namei.c:4536 [inline]
 __se_sys_symlink fs/namei.c:4534 [inline]
 __x64_sys_symlink+0x79/0xa0 fs/namei.c:4534
 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: 0033:0x7fbfa6a7cee9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbfa77a80c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007fbfa6babf80 RCX: 00007fbfa6a7cee9
RDX: 0000000000000000 RSI: 0000000020000e40 RDI: 0000000020001640
RBP: 00007fbfa6ac949e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007fbfa6babf80 R15: 00007ffe2b646ac8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xc5b pfn:0x663b7
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea000198ee08 ffffea000198ed88 0000000000000000
raw: 0000000000000c5b 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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 8563, tgid 8557 (syz-executor.1), ts 265106157810, free_ts 265480339103
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1468
 prep_new_page mm/page_alloc.c:1476 [inline]
 get_page_from_freelist+0x136a/0x2df0 mm/page_alloc.c:3402
 __alloc_pages_noprof+0x22b/0x2460 mm/page_alloc.c:4660
 alloc_pages_mpol_noprof+0x275/0x610 mm/mempolicy.c:2265
 shmem_alloc_folio+0x114/0x150 mm/shmem.c:1628
 shmem_alloc_and_add_folio+0x14f/0x790 mm/shmem.c:1668
 shmem_get_folio_gfp+0x687/0x13d0 mm/shmem.c:2055
 shmem_get_folio mm/shmem.c:2160 [inline]
 shmem_write_begin+0x15a/0x360 mm/shmem.c:2743
 generic_perform_write+0x272/0x620 mm/filemap.c:4015
 shmem_file_write_iter+0x114/0x140 mm/shmem.c:2919
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x6b6/0x1140 fs/read_write.c:590
 ksys_write+0x12f/0x260 fs/read_write.c:643
 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 8563 tgid 8557 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1088 [inline]
 free_unref_folios+0x991/0x1310 mm/page_alloc.c:2614
 folios_put_refs+0x487/0x6d0 mm/swap.c:1024
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x5a1/0x1160 mm/shmem.c:1005
 shmem_truncate_range mm/shmem.c:1114 [inline]
 shmem_evict_inode+0x3a3/0xbb0 mm/shmem.c:1242
 evict+0x2ed/0x6c0 fs/inode.c:667
 iput_final fs/inode.c:1741 [inline]
 iput.part.0+0x5a8/0x7f0 fs/inode.c:1767
 iput+0x5c/0x80 fs/inode.c:1757
 dentry_unlink_inode+0x295/0x480 fs/dcache.c:400
 __dentry_kill+0x1d0/0x600 fs/dcache.c:603
 dput.part.0+0x4b1/0x9b0 fs/dcache.c:845
 dput+0x1f/0x30 fs/dcache.c:835
 __fput+0x54e/0xbb0 fs/file_table.c:430
 __fput_sync+0x47/0x50 fs/file_table.c:507
 __do_sys_close fs/open.c:1555 [inline]
 __se_sys_close fs/open.c:1540 [inline]
 __x64_sys_close+0x86/0x100 fs/open.c:1540
 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

Memory state around the buggy address:
 ffff8880663b6f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880663b7000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880663b7080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff8880663b7100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880663b7180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================