[syzbot] [bluetooth?] [bcachefs?] KASAN: slab-use-after-free Read in hci_uart_write_work

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=174b07d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
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
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127ece8c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3f31a806.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7304d62ced97/vmlinux-3f31a806.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4913df6ab730/bzImage-3f31a806.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/bb03f46b9e61/mount_5.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fde6bd...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in hci_uart_write_work+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
Read of size 8 at addr ffff8880555a35d8 by task kworker/0:7/5631

CPU: 0 UID: 0 PID: 5631 Comm: kworker/0:7 Not tainted 6.16.0-rc5-syzkaller-00266-g3f31a806a62e #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+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
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 54:
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:107 [inline]
hci_uart_write_work+0x24a/0x550 drivers/bluetooth/hci_ldisc.c:161
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 ffff8880555a3500
which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 216 bytes inside of
freed 240-byte region [ffff8880555a3500, ffff8880555a35f0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x555a3
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000000 ffff8880304e0b40 dead000000000100 dead000000000122
raw: 0000000000000000 00000000000c000c 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 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5474, tgid 5474 (syz-executor), ts 183992405509, free_ts 181552341552
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]
nlmsg_new include/net/netlink.h:1041 [inline]
inet_netconf_notify_devconf+0x173/0x240 net/ipv4/devinet.c:2210
__devinet_sysctl_register+0x3f6/0x470 net/ipv4/devinet.c:2684
devinet_sysctl_register+0x187/0x200 net/ipv4/devinet.c:2718
inetdev_init+0x2b4/0x500 net/ipv4/devinet.c:291
inetdev_event+0x301/0x15b0 net/ipv4/devinet.c:1591
notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
call_netdevice_notifiers net/core/dev.c:2282 [inline]
register_netdevice+0x1608/0x1ae0 net/core/dev.c:11143
team_newlink+0x114/0x160 drivers/net/team/team_core.c:2231
page last free pid 5407 tgid 5407 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
vfree+0x25a/0x400 mm/vmalloc.c:3434
kcov_put kernel/kcov.c:439 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:535
__fput+0x449/0xa70 fs/file_table.c:465
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x22e0 kernel/exit.c:964
do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
get_signal+0x1286/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:111
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff8880555a3480: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
ffff8880555a3500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880555a3580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
^
ffff8880555a3600: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
ffff8880555a3680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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If you want to undo deduplication, reply with:
#syz undup

[Hillf Danton]

> Date: Mon, 14 Jul 2025 10:09:31 -0700 [thread overview]

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=174b07d4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
> dashboard link: https://syzkaller.appspot.com/bug?extid=fde6bd779f78e6e0992e

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127ece8c580000

#syz test

--- x/drivers/bluetooth/hci_uart.h
+++ y/drivers/bluetooth/hci_uart.h
@@ -69,6 +69,7 @@ struct hci_uart {
unsigned long hdev_flags;

struct work_struct init_ready;
+ struct mutex write_mutex;
struct work_struct write_work;

const struct hci_uart_proto *proto;
--- x/drivers/bluetooth/hci_ldisc.c
+++ y/drivers/bluetooth/hci_ldisc.c
@@ -154,6 +154,7 @@ static void hci_uart_write_work(struct w
/* REVISIT: should we cope with bad skbs or ->write() returning
* and error value ?
*/
+ mutex_lock(&hu->write_mutex);

restart:
clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
@@ -180,6 +181,7 @@ restart:
goto restart;

wake_up_bit(&hu->tx_state, HCI_UART_SENDING);
+ mutex_unlock(&hu->write_mutex);
}

void hci_uart_init_work(struct work_struct *work)
@@ -515,6 +517,7 @@ static int hci_uart_tty_open(struct tty_

INIT_WORK(&hu->init_ready, hci_uart_init_work);
INIT_WORK(&hu->write_work, hci_uart_write_work);
+ mutex_init(&hu->write_mutex);

/* Flush any pending characters in the driver */
tty_driver_flush_buffer(tty);
--

[syzbot]

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+0x337/0x5c0 drivers/bluetooth/hci_ldisc.c:166
Read of size 8 at addr ffff888011e31c18 by task kworker/0:8/6224

CPU: 0 UID: 0 PID: 6224 Comm: kworker/0:8 Not tainted 6.16.0-rc6-syzkaller-g347e9f5043c8-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+0x337/0x5c0 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 55:

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:107 [inline]

hci_uart_write_work+0x2ad/0x5c0 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 ffff888011e31b40

which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 216 bytes inside of

freed 240-byte region [ffff888011e31b40, ffff888011e31c30)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11e31
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88801bef7b40 dead000000000100 dead000000000122

raw: 0000000000000000 00000000000c000c 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 5346, tgid 5346 (syz-executor), ts 93020059691, free_ts 92682760557

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_pages_slowpath+0x2fe/0xce0 mm/page_alloc.c:4490
__alloc_frozen_pages_noprof+0x319/0x370 mm/page_alloc.c:4972

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]
nlmsg_new include/net/netlink.h:1041 [inline]

inet6_rt_notify+0x165/0x430 net/ipv6/route.c:6334
fib6_del_route net/ipv6/ip6_fib.c:2058 [inline]
fib6_del+0x1094/0x1550 net/ipv6/ip6_fib.c:2093
fib6_clean_node+0x29f/0x590 net/ipv6/ip6_fib.c:2255
fib6_walk_continue+0x67b/0x910 net/ipv6/ip6_fib.c:2177
fib6_walk+0x149/0x290 net/ipv6/ip6_fib.c:2225
fib6_clean_tree net/ipv6/ip6_fib.c:2305 [inline]
__fib6_clean_all+0x234/0x380 net/ipv6/ip6_fib.c:2321
rt6_sync_down_dev net/ipv6/route.c:5004 [inline]
rt6_disable_ip+0x120/0x720 net/ipv6/route.c:5009
page last free pid 5360 tgid 5360 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

discard_slab mm/slub.c:2717 [inline]
__put_partials+0x161/0x1c0 mm/slub.c:3186
put_cpu_partial+0x17c/0x250 mm/slub.c:3261
__slab_free+0x2f7/0x400 mm/slub.c:4513
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:329

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]

__do_kmalloc_node mm/slub.c:4327 [inline]
__kmalloc_noprof+0x224/0x4f0 mm/slub.c:4340
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
tomoyo_encode2 security/tomoyo/realpath.c:45 [inline]
tomoyo_encode+0x28b/0x550 security/tomoyo/realpath.c:80
tomoyo_mount_acl security/tomoyo/mount.c:150 [inline]
tomoyo_mount_permission+0x44d/0x970 security/tomoyo/mount.c:237
security_sb_mount+0xec/0x350 security/security.c:1570
path_mount+0xbc/0xfe0 fs/namespace.c:4168
do_mount fs/namespace.c:4239 [inline]
__do_sys_mount fs/namespace.c:4450 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4427
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:

ffff888011e31b00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff888011e31b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888011e31c00: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
^
ffff888011e31c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888011e31d00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
==================================================================


Tested on:

commit: 347e9f50 Linux 6.16-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15a770f0580000
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=12e00382580000

[Hillf Danton]

> Date: Mon, 14 Jul 2025 10:09:31 -0700 [thread overview]

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=174b07d4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
> dashboard link: https://syzkaller.appspot.com/bug?extid=fde6bd779f78e6e0992e

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127ece8c580000

#syz test

--- x/drivers/bluetooth/hci_ldisc.c
+++ y/drivers/bluetooth/hci_ldisc.c
@@ -100,13 +100,9 @@ static inline struct sk_buff *hci_uart_d
struct sk_buff *skb = hu->tx_skb;

if (!skb) {
- percpu_down_read(&hu->proto_lock);
-
if (test_bit(HCI_UART_PROTO_READY, &hu->flags) ||
test_bit(HCI_UART_PROTO_INIT, &hu->flags))
skb = hu->proto->dequeue(hu);
-
- percpu_up_read(&hu->proto_lock);
} else {
hu->tx_skb = NULL;
}
@@ -154,6 +150,11 @@ static void hci_uart_write_work(struct w

/* REVISIT: should we cope with bad skbs or ->write() returning
* and error value ?
*/

+ percpu_down_read(&hu->proto_lock);
+ if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
+ percpu_up_read(&hu->proto_lock);
+ return;
+ }

restart:
clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
@@ -179,6 +180,7 @@ restart:
if (test_bit(HCI_UART_TX_WAKEUP, &hu->tx_state))
goto restart;

+ percpu_up_read(&hu->proto_lock);
wake_up_bit(&hu->tx_state, HCI_UART_SENDING);
}

--

[syzbot]

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

[Hillf Danton]

> Date: Mon, 14 Jul 2025 10:09:31 -0700 [thread overview]

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=174b07d4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
> dashboard link: https://syzkaller.appspot.com/bug?extid=fde6bd779f78e6e0992e

@@ -231,9 +233,12 @@ static int hci_uart_flush(struct hci_dev

BT_DBG("hdev %p tty %p", hdev, tty);

+ percpu_down_write(&hu->proto_lock);
if (hu->tx_skb) {
- kfree_skb(hu->tx_skb); hu->tx_skb = NULL;
+ kfree_skb(hu->tx_skb);
+ hu->tx_skb = NULL;
}
+ percpu_up_write(&hu->proto_lock);

/* Flush any pending characters in the driver and discipline. */
tty_ldisc_flush(tty);
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+fde6bd...@syzkaller.appspotmail.com
Tested-by: syzbot+fde6bd...@syzkaller.appspotmail.com

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=15adf0f0580000

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=1292d18c580000

Note: testing is done by a robot and is best-effort only.

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject:
Author: kent.ov...@linux.dev

#syz set subsystems: bluetooth

[Ivan Pravdin]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master

Ivan Pravdin

[syzbot]

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+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
Read of size 8 at addr ffff888058e8c0d8 by task kworker/0:4/5440

CPU: 0 UID: 0 PID: 5440 Comm: kworker/0:4 Not tainted 6.15.0-rc6-syzkaller-01366-g0ba714749722 #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:408 [inline]
print_report+0xd2/0x2b0 mm/kasan/report.c:521
kasan_report+0x118/0x150 mm/kasan/report.c:634

hci_uart_write_work+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
process_one_work kernel/workqueue.c:3238 [inline]

process_scheduled_works+0xade/0x17a0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 5456:

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:4147 [inline]
slab_alloc_node mm/slub.c:4196 [inline]
kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4248
__alloc_skb+0x112/0x2d0 net/core/skbuff.c:659
alloc_skb include/linux/skbuff.h:1337 [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:107 [inline]
hci_uart_write_work+0x247/0x550 drivers/bluetooth/hci_ldisc.c:161
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0xade/0x17a0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888058e8c000

which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 216 bytes inside of

freed 240-byte region [ffff888058e8c000, ffff888058e8c0f0)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x58e8c
anon flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000000 ffff888030afe8c0 0000000000000000 dead000000000001
raw: 0000000000000000 00000000000c000c 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 13, tgid 13 (kworker/u4:1), ts 191152770378, free_ts 191108105126
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1714
prep_new_page mm/page_alloc.c:1722 [inline]
get_page_from_freelist+0x21e0/0x22c0 mm/page_alloc.c:3684
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4966
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2301
alloc_slab_page mm/slub.c:2450 [inline]
allocate_slab+0x8a/0x3b0 mm/slub.c:2618
new_slab mm/slub.c:2672 [inline]
___slab_alloc+0xbfc/0x1480 mm/slub.c:3858
__slab_alloc mm/slub.c:3948 [inline]
__slab_alloc_node mm/slub.c:4023 [inline]
slab_alloc_node mm/slub.c:4184 [inline]
kmem_cache_alloc_node_noprof+0x280/0x3c0 mm/slub.c:4248
__alloc_skb+0x112/0x2d0 net/core/skbuff.c:659
alloc_skb include/linux/skbuff.h:1337 [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+0xade/0x17a0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page last free pid 6142 tgid 6140 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1258 [inline]
__free_frozen_pages+0xc6e/0xe50 mm/page_alloc.c:2721
vfree+0x1a6/0x330 mm/vmalloc.c:3384
n_tty_close+0x159/0x1d0 drivers/tty/n_tty.c:1883
tty_set_ldisc+0x33f/0x560 drivers/tty/tty_ldisc.c:557
tty_ioctl+0xc38/0xde0 drivers/tty/tty_io.c:2738
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x220 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:

ffff888058e8bf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888058e8c000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888058e8c080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
^
ffff888058e8c100: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff888058e8c180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


Tested on:

commit: 0ba71474 Bluetooth: hci_event: Mask data status from L..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=119af722580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1fa9d0bcb4675c74

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

Note: no patches were applied.