u64s 7 type dirent 4096:35085515490358056:U32_MAX len 0 ver 0: file3 -> 536870913 type reg, fixing
bcachefs (loop0): directory with missing backpointer
  u64s 7 type dirent 4096:68795212746880106:U32_MAX len 0 ver 0: file0 -> 4098 type dir
  inum: 4098:4294967295 
    mode=40600
    flags=(4300000)
    journal_seq=18
    hash_seed=e442b1f54fa0ad8d
    hash_type=siphash
    bi_size=0
    bi_sectors=0
    bi_version=0
    bi_atime=31031626331391887
    bi_ctime=31031626331391887
    bi_mtime=31031626331391887
    bi_otime=31031626331391887
    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
    bi_casefold=0, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 8 type dirent 4096:851866006260432107:U32_MAX len 0 ver 0: lost+found -> 4097 type dir, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 8 type dirent 4096:6331225265350904928:U32_MAX len 0 ver 0: file.cold -> 536870914 type reg, fixing
bcachefs (loop0): fsck counted subdirectories wrong for inum 4096:4294967295: got 2 should be 1
bcachefs (loop0): directory 4096:4294967295 with wrong i_nlink: got 0, should be 1, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 7 type dirent 4098:3004007168038595019:U32_MAX len 0 ver 0: file0 -> 4099 type reg, fixing
bcachefs (loop0): dirent points to missing inode:
  u64s 7 type dirent 4098:3847204686676512778:U32_MAX len 0 ver 0: file1 -> 4100 type lnk, fixing
==================================================================
BUG: KASAN: use-after-free in check_dirent fs/bcachefs/fsck.c:2247 [inline]
BUG: KASAN: use-after-free in bch2_check_dirents+0x1bac/0x2460 fs/bcachefs/fsck.c:2272
Read of size 1 at addr ffff888055980198 by task syz.0.0/5318

CPU: 0 UID: 0 PID: 5318 Comm: syz.0.0 Not tainted 6.15.0-rc3-syzkaller-00342-g5bc1018675ec #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_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xb4/0x290 mm/kasan/report.c:521
 kasan_report+0x118/0x150 mm/kasan/report.c:634
 check_dirent fs/bcachefs/fsck.c:2247 [inline]
 bch2_check_dirents+0x1bac/0x2460 fs/bcachefs/fsck.c:2272
 bch2_run_recovery_pass+0xdf/0x1d0 fs/bcachefs/recovery_passes.c:227
 bch2_run_recovery_passes+0x2a0/0xdb0 fs/bcachefs/recovery_passes.c:280
 bch2_fs_recovery+0x26c8/0x37b0 fs/bcachefs/recovery.c:974
 bch2_fs_start+0x70b/0xae0 fs/bcachefs/super.c:1083
 bch2_fs_get_tree+0xd99/0x1340 fs/bcachefs/fs.c:2570
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1759
 do_new_mount+0x24a/0xa40 fs/namespace.c:3884
 do_mount fs/namespace.c:4224 [inline]
 __do_sys_mount fs/namespace.c:4435 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4412
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6cddd9010a
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:00007f6cda1f4e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f6cda1f4ef0 RCX: 00007f6cddd9010a
RDX: 0000200000000000 RSI: 0000200000000040 RDI: 00007f6cda1f4eb0
RBP: 0000200000000000 R08: 00007f6cda1f4ef0 R09: 0000000001000001
R10: 0000000001000001 R11: 0000000000000246 R12: 0000200000000040
R13: 00007f6cda1f4eb0 R14: 0000000000005968 R15: 0000200000000300
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x55980
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f0(buddy)
raw: 04fff00000000000 ffffea0001551808 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 5318, tgid 5316 (syz.0.0), ts 69691422407, free_ts 69833851545
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1d8/0x230 mm/page_alloc.c:1718
 prep_new_page mm/page_alloc.c:1726 [inline]
 get_page_from_freelist+0x21ce/0x22b0 mm/page_alloc.c:3688
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4970
 __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:5004
 __alloc_pages_node_noprof include/linux/gfp.h:284 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:311 [inline]
 ___kmalloc_large_node+0x85/0x200 mm/slub.c:4285
 __kmalloc_large_node_noprof+0x18/0x90 mm/slub.c:4313
 __do_kmalloc_node mm/slub.c:4329 [inline]
 __kvmalloc_node_noprof+0x74/0x5e0 mm/slub.c:5026
 btree_bounce_alloc fs/bcachefs/btree_io.c:124 [inline]
 btree_node_sort+0x65d/0x1790 fs/bcachefs/btree_io.c:323
 bch2_btree_post_write_cleanup+0x11f/0xab0 fs/bcachefs/btree_io.c:2508
 bch2_btree_node_write_trans+0x17b/0x760 fs/bcachefs/btree_io.c:2577
 btree_node_write_if_need fs/bcachefs/btree_io.h:157 [inline]
 __btree_node_flush+0x323/0x430 fs/bcachefs/btree_trans_commit.c:253
 bch2_btree_node_flush0+0x27/0x40 fs/bcachefs/btree_trans_commit.c:262
 journal_flush_pins+0x8e0/0xe90 fs/bcachefs/journal_reclaim.c:592
 journal_flush_pins_or_still_flushing fs/bcachefs/journal_reclaim.c:862 [inline]
 journal_flush_done+0x112/0x810 fs/bcachefs/journal_reclaim.c:880
 bch2_journal_flush_pins+0xdc/0x250 fs/bcachefs/journal_reclaim.c:912
 bch2_journal_flush_all_pins fs/bcachefs/journal_reclaim.h:76 [inline]
 bch2_fs_recovery+0x2550/0x37b0 fs/bcachefs/recovery.c:958
page last free pid 5318 tgid 5316 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1262 [inline]
 __free_pages_ok+0x916/0xac0 mm/page_alloc.c:1438
 __folio_put+0x21b/0x2c0 mm/swap.c:112
 folio_put include/linux/mm.h:1580 [inline]
 free_large_kmalloc+0x145/0x200 mm/slub.c:4781
 btree_bounce_free fs/bcachefs/btree_io.c:112 [inline]
 btree_node_sort+0x1149/0x1790 fs/bcachefs/btree_io.c:380
 bch2_btree_post_write_cleanup+0x11f/0xab0 fs/bcachefs/btree_io.c:2508
 bch2_btree_node_prep_for_write+0x341/0x660 fs/bcachefs/btree_trans_commit.c:93
 bch2_trans_lock_write+0x669/0xbb0 fs/bcachefs/btree_trans_commit.c:129
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:840 [inline]
 __bch2_trans_commit+0x2cb3/0x8ae0 fs/bcachefs/btree_trans_commit.c:1050
 bch2_trans_commit fs/bcachefs/btree_update.h:195 [inline]
 check_dirent fs/bcachefs/fsck.c:2242 [inline]
 bch2_check_dirents+0x19ae/0x2460 fs/bcachefs/fsck.c:2272
 bch2_run_recovery_pass+0xdf/0x1d0 fs/bcachefs/recovery_passes.c:227
 bch2_run_recovery_passes+0x2a0/0xdb0 fs/bcachefs/recovery_passes.c:280
 bch2_fs_recovery+0x26c8/0x37b0 fs/bcachefs/recovery.c:974
 bch2_fs_start+0x70b/0xae0 fs/bcachefs/super.c:1083
 bch2_fs_get_tree+0xd99/0x1340 fs/bcachefs/fs.c:2570
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1759
 do_new_mount+0x24a/0xa40 fs/namespace.c:3884

Memory state around the buggy address:
 ffff888055980080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888055980100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888055980180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888055980200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888055980280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================