bcachefs (loop0): error validating btree node at btree extents level 0/0
  u64s 11 type btree_ptr_v2 SPOS_MAX len 0 ver 0: seq c6c25c03258c59c5 written 48 min_key 0:36028797018963968:0 durability: 1 ptr: 0:27:0 gen 0  
  node offset 8/48 bset u64s 2088 bset byte offset 360: bad k->u64s 0 (min 3 max 253), fixing
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BUG: KASAN: use-after-free in bkey_packed_valid+0x488/0x6c0 fs/bcachefs/btree_io.c:865
Read of size 1 at addr ffff888047ca0000 by task kworker/0:1H/37

CPU: 0 UID: 0 PID: 37 Comm: kworker/0:1H Not tainted 6.14.0-rc5-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: bcachefs_btree_read_complete btree_node_read_work
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
 bkey_packed_valid+0x488/0x6c0 fs/bcachefs/btree_io.c:865
 validate_bset_keys+0xeb5/0x1af0 fs/bcachefs/btree_io.c:987
 bch2_btree_node_read_done+0x2298/0x6180 fs/bcachefs/btree_io.c:1164
 btree_node_read_work+0x6dc/0x1380 fs/bcachefs/btree_io.c:1358
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xabe/0x18e0 kernel/workqueue.c:3319
 worker_thread+0x870/0xd30 kernel/workqueue.c:3400
 kthread+0x7a9/0x920 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x47ca0
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea00011f2848 ffffea00011f1fc8 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff888047c9ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888047c9ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888047ca0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff888047ca0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888047ca0100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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