bcachefs (loop0): scanning for missing backpointers in 1/128 buckets
 done
bcachefs (loop0): check_snapshots... done
bcachefs (loop0): check_subvols... done
bcachefs (loop0): check_inodes... done
bcachefs (loop0): check_dirents...
bcachefs (loop0): dirent points to missing inode:
  u64s 7 type dirent 4096:508771216775134759:U32_MAX len 0 ver 0: file3 -> 1073741825 type reg, fixing
bcachefs (loop0): directory with missing backpointer
  u64s 7 type dirent 4096:1316329587870451630:U32_MAX len 0 ver 0: file0 -> 4098 type dir
  inum: 4098:4294967295 
    mode=40600
    flags=(4300000)
    journal_seq=23
    hash_seed=d5d2eed0ca556c61
    hash_type=siphash
    bi_size=0
    bi_sectors=0
    bi_version=0
    bi_atime=29334185553495702
    bi_ctime=29334185553495702
    bi_mtime=29334185553495702
    bi_otime=29334185553495702
    bi_uid=0
    bi_gid=0
    bi_nlink=0
    bi_generation=0
    bi_dev=0
    bi_data_checksum=0
    bi_compression=0
    bi_project=0
    bi_background_compression=0
    bi_data_replicas=0
    bi_promote_target=0
    bi_foreground_target=0
    bi_background_target=0
    bi_erasure_code=0
    bi_fields_set=0
    bi_dir=0
    bi_dir_offset=0
    bi_subvol=0
    bi_parent_subvol=0
    bi_nocow=0
    bi_depth=0
    bi_inodes_32bit=0, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 7 type dirent 4096:3733564823327202707:U32_MAX len 0 ver 0: file1— -> 1073741824 type reg, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 7 type dirent 4096:5937062504331745319:U32_MAX len 0 ver 0: file2 -> 1073741825 type reg, fixing
==================================================================
BUG: KASAN: use-after-free in check_dirent fs/bcachefs/fsck.c:2205 [inline]
BUG: KASAN: use-after-free in bch2_check_dirents+0x2aac/0x3b90 fs/bcachefs/fsck.c:2230
Read of size 1 at addr ffff8880569c0138 by task syz.0.0/5324

CPU: 0 UID: 0 PID: 5324 Comm: syz.0.0 Not tainted 6.15.0-rc1-syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x16e/0x5b0 mm/kasan/report.c:521
 kasan_report+0x143/0x180 mm/kasan/report.c:634
 check_dirent fs/bcachefs/fsck.c:2205 [inline]
 bch2_check_dirents+0x2aac/0x3b90 fs/bcachefs/fsck.c:2230
 bch2_run_recovery_pass+0xf0/0x1e0 fs/bcachefs/recovery_passes.c:226
 bch2_run_recovery_passes+0x2ad/0xa90 fs/bcachefs/recovery_passes.c:285
 bch2_fs_recovery+0x2c65/0x3e20 fs/bcachefs/recovery.c:973
 bch2_fs_start+0x310/0x620 fs/bcachefs/super.c:1069
 bch2_fs_get_tree+0x113e/0x18f0 fs/bcachefs/fs.c:2253
 vfs_get_tree+0x90/0x2b0 fs/super.c:1759
 do_new_mount+0x2cf/0xb70 fs/namespace.c:3879
 do_mount fs/namespace.c:4219 [inline]
 __do_sys_mount fs/namespace.c:4430 [inline]
 __se_sys_mount+0x38c/0x400 fs/namespace.c:4407
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe548d8e90a
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007fe5451ece68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fe5451ecef0 RCX: 00007fe548d8e90a
RDX: 000020000000f640 RSI: 0000200000000140 RDI: 00007fe5451eceb0
RBP: 000020000000f640 R08: 00007fe5451ecef0 R09: 0000000000000008
R10: 0000000000000008 R11: 0000000000000246 R12: 0000200000000140
R13: 00007fe5451eceb0 R14: 000000000000f613 R15: 0000200000000180
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x569c0
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f0(buddy)
raw: 04fff00000000000 ffffea000159b008 ffff88805ffd6f08 0000000000000000
raw: 0000000000000000 0000000000000005 00000000f0000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 5, migratetype Unmovable, gfp_mask 0x52800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP), pid 5324, tgid 5323 (syz.0.0), ts 83451948678, free_ts 83912118963
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1717
 prep_new_page mm/page_alloc.c:1725 [inline]
 get_page_from_freelist+0x352b/0x36c0 mm/page_alloc.c:3652
 __alloc_frozen_pages_noprof+0x211/0x5b0 mm/page_alloc.c:4934
 __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:4968
 __alloc_pages_node_noprof include/linux/gfp.h:284 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:311 [inline]
 ___kmalloc_large_node+0x92/0x210 mm/slub.c:4275
 __kmalloc_large_node_noprof+0x1a/0x80 mm/slub.c:4303
 __do_kmalloc_node mm/slub.c:4319 [inline]
 __kvmalloc_node_noprof+0x7c/0x5a0 mm/slub.c:5016
 btree_bounce_alloc fs/bcachefs/btree_io.c:124 [inline]
 btree_node_sort+0x67c/0x1870 fs/bcachefs/btree_io.c:323
 bch2_btree_post_write_cleanup+0x11a/0xaa0 fs/bcachefs/btree_io.c:2508
 bch2_btree_node_write_trans+0x18a/0x7a0 fs/bcachefs/btree_io.c:2577
 btree_node_write_if_need fs/bcachefs/btree_io.h:157 [inline]
 __btree_node_flush+0x3a1/0x470 fs/bcachefs/btree_trans_commit.c:253
 bch2_btree_node_flush1+0x2a/0x40 fs/bcachefs/btree_trans_commit.c:267
 journal_flush_pins+0x89b/0xe40 fs/bcachefs/journal_reclaim.c:589
 journal_flush_pins_or_still_flushing fs/bcachefs/journal_reclaim.c:859 [inline]
 journal_flush_done+0x107/0x820 fs/bcachefs/journal_reclaim.c:877
 bch2_journal_flush_pins+0x23a/0x3c0 fs/bcachefs/journal_reclaim.c:909
 bch2_journal_flush_all_pins fs/bcachefs/journal_reclaim.h:76 [inline]
 bch2_fs_recovery+0x2af1/0x3e20 fs/bcachefs/recovery.c:957
page last free pid 5324 tgid 5323 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1262 [inline]
 __free_pages_ok+0xb1d/0xda0 mm/page_alloc.c:1437
 __folio_put+0x2b5/0x360 mm/swap.c:112
 folio_put include/linux/mm.h:1563 [inline]
 free_large_kmalloc+0x143/0x1e0 mm/slub.c:4771
 kfree+0x216/0x430 mm/slub.c:4839
 btree_bounce_free fs/bcachefs/btree_io.c:112 [inline]
 btree_node_sort+0x1124/0x1870 fs/bcachefs/btree_io.c:380
 bch2_btree_post_write_cleanup+0x11a/0xaa0 fs/bcachefs/btree_io.c:2508
 bch2_btree_node_prep_for_write+0x35a/0x670 fs/bcachefs/btree_trans_commit.c:93
 bch2_trans_lock_write+0x66f/0xb60 fs/bcachefs/btree_trans_commit.c:129
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:840 [inline]
 __bch2_trans_commit+0x3252/0x9da0 fs/bcachefs/btree_trans_commit.c:1050
 bch2_trans_commit fs/bcachefs/btree_update.h:195 [inline]
 check_dirent fs/bcachefs/fsck.c:2200 [inline]
 bch2_check_dirents+0x2801/0x3b90 fs/bcachefs/fsck.c:2230
 bch2_run_recovery_pass+0xf0/0x1e0 fs/bcachefs/recovery_passes.c:226
 bch2_run_recovery_passes+0x2ad/0xa90 fs/bcachefs/recovery_passes.c:285
 bch2_fs_recovery+0x2c65/0x3e20 fs/bcachefs/recovery.c:973
 bch2_fs_start+0x310/0x620 fs/bcachefs/super.c:1069
 bch2_fs_get_tree+0x113e/0x18f0 fs/bcachefs/fs.c:2253
 vfs_get_tree+0x90/0x2b0 fs/super.c:1759

Memory state around the buggy address:
 ffff8880569c0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880569c0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880569c0100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                        ^
 ffff8880569c0180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880569c0200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================