linux-kernel - Re: [syzbot] [bluetooth?] [bcachefs?] KASAN: slab-use-after-free Read in hci_uart_write

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Message-ID: <6875de38.a00a0220.3af5df.0000.GAE@google.com>
Date: Mon, 14 Jul 2025 21:51:04 -0700
From: syzbot <syzbot+fde6bd779f78e6e0992e@...kaller.appspotmail.com>
To: hdanton@...a.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bluetooth?] [bcachefs?] KASAN: slab-use-after-free Read
 in hci_uart_write_work

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in hci_uart_write_work

==================================================================
BUG: KASAN: slab-use-after-free in hci_uart_write_work+0x31b/0x580 drivers/bluetooth/hci_ldisc.c:166
Read of size 8 at addr ffff888054b5ed58 by task kworker/0:7/6055

CPU: 0 UID: 0 PID: 6055 Comm: kworker/0:7 Not tainted 6.16.0-rc6-syzkaller-g155a3c003e55-dirty #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
Workqueue: events hci_uart_write_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x230 mm/kasan/report.c:480
 kasan_report+0x118/0x150 mm/kasan/report.c:593
 hci_uart_write_work+0x31b/0x580 drivers/bluetooth/hci_ldisc.c:166
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 6055:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4249
 __alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
 alloc_skb include/linux/skbuff.h:1336 [inline]
 h5_prepare_pkt+0x184/0x530 drivers/bluetooth/hci_h5.c:702
 h5_dequeue+0x197/0x790 drivers/bluetooth/hci_h5.c:761
 hci_uart_dequeue drivers/bluetooth/hci_ldisc.c:105 [inline]
 hci_uart_write_work+0x29a/0x580 drivers/bluetooth/hci_ldisc.c:162
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888054b5ec80
 which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 216 bytes inside of
 freed 240-byte region [ffff888054b5ec80, ffff888054b5ed70)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888054b5e140 pfn:0x54b5e
flags: 0x4fff00000000200(workingset|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000200 ffff8880304efb40 ffffea0001253bd0 ffffea00016134d0
raw: ffff888054b5e140 00000000000c000a 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 3020, tgid 3020 (kworker/u4:11), ts 227043981111, free_ts 226252562525
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
 alloc_slab_page mm/slub.c:2451 [inline]
 allocate_slab+0x8a/0x3b0 mm/slub.c:2619
 new_slab mm/slub.c:2673 [inline]
 ___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
 __slab_alloc mm/slub.c:3949 [inline]
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 kmem_cache_alloc_node_noprof+0x280/0x3c0 mm/slub.c:4249
 __alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
 alloc_skb include/linux/skbuff.h:1336 [inline]
 nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
 nsim_dev_trap_report_work+0x29a/0xb80 drivers/net/netdevsim/dev.c:851
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page last free pid 15 tgid 15 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1248 [inline]
 __free_frozen_pages+0xc71/0xe70 mm/page_alloc.c:2706
 pagetable_free include/linux/mm.h:2884 [inline]
 pagetable_dtor_free include/linux/mm.h:2982 [inline]
 __tlb_remove_table+0x2d2/0x3b0 include/asm-generic/tlb.h:220
 __tlb_remove_table_free mm/mmu_gather.c:227 [inline]
 tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
 rcu_do_batch kernel/rcu/tree.c:2576 [inline]
 rcu_core+0xca8/0x1710 kernel/rcu/tree.c:2832
 handle_softirqs+0x286/0x870 kernel/softirq.c:579
 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
 smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:164
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888054b5ec00: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
 ffff888054b5ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888054b5ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
                                                    ^
 ffff888054b5ed80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
 ffff888054b5ee00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit:         155a3c00 Merge tag 'for-6.16/dm-fixes-2' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c2f0f0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f62a2ef17395702a
dashboard link: https://syzkaller.appspot.com/bug?extid=fde6bd779f78e6e0992e
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17c90382580000