linux-kernel - Re: [PATCH v3] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter

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Message-ID: <a408927c-3743-71de-b806-87fd404bb9a2@salutedevices.com>
Date: Mon, 30 Jun 2025 14:08:02 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz
	<luiz.dentz@...il.com>
CC: <oxffffaa@...il.com>, <linux-bluetooth@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kernel@...utedevices.com>
Subject: Re: [PATCH v3] Bluetooth: hci_sync: fix double free in
 'hci_discovery_filter_clear()'

Hi, sorry, 2 weeks, pls ping

Thanks

On 15.06.2025 20:17, Arseniy Krasnov wrote:
> Function 'hci_discovery_filter_clear()' frees 'uuids' array and then
> sets it to NULL. There is a tiny chance of the following race:
> 
> 'hci_cmd_sync_work()'
> 
>  'update_passive_scan_sync()'
> 
>    'hci_update_passive_scan_sync()'
> 
>      'hci_discovery_filter_clear()'
>        kfree(uuids);
> 
>        <-------------------------preempted-------------------------------->
>                                            'start_service_discovery()'
> 
>                                              'hci_discovery_filter_clear()'
>                                                kfree(uuids); // DOUBLE FREE
> 
>        <-------------------------preempted-------------------------------->
> 
>       uuids = NULL;
> 
> To fix it let's add locking around 'kfree()' call and NULL pointer
> assignment. Otherwise the following backtrace fires:
> 
> [ ] ------------[ cut here ]------------
> [ ] kernel BUG at mm/slub.c:547!
> [ ] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
> [ ] CPU: 3 UID: 0 PID: 246 Comm: bluetoothd Tainted: G O 6.12.19-kernel #1
> [ ] Tainted: [O]=OOT_MODULE
> [ ] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [ ] pc : __slab_free+0xf8/0x348
> [ ] lr : __slab_free+0x48/0x348
> ...
> [ ] Call trace:
> [ ]  __slab_free+0xf8/0x348
> [ ]  kfree+0x164/0x27c
> [ ]  start_service_discovery+0x1d0/0x2c0
> [ ]  hci_sock_sendmsg+0x518/0x924
> [ ]  __sock_sendmsg+0x54/0x60
> [ ]  sock_write_iter+0x98/0xf8
> [ ]  do_iter_readv_writev+0xe4/0x1c8
> [ ]  vfs_writev+0x128/0x2b0
> [ ]  do_writev+0xfc/0x118
> [ ]  __arm64_sys_writev+0x20/0x2c
> [ ]  invoke_syscall+0x68/0xf0
> [ ]  el0_svc_common.constprop.0+0x40/0xe0
> [ ]  do_el0_svc+0x1c/0x28
> [ ]  el0_svc+0x30/0xd0
> [ ]  el0t_64_sync_handler+0x100/0x12c
> [ ]  el0t_64_sync+0x194/0x198
> [ ] Code: 8b0002e6 eb17031f 54fffbe1 d503201f (d4210000) 
> [ ] ---[ end trace 0000000000000000 ]---
> 
> Fixes: ad383c2c65a5 ("Bluetooth: hci_sync: Enable advertising when LL privacy is enabled")
> Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
> ---
>  Changelog v1->v2:
>  * Don't call 'hci_dev_lock()' in 'update_passive_scan_sync()' as it
>    triggers deadlock. Instead of that - add spinlock which protects
>    freeing code.
>  Changelog v2->v3:
>  * Rebase on current 'bluetooth' repo due to fuzz.
> 
>  include/net/bluetooth/hci_core.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
> index 54bfeeaa09959..f8eeb15acdcfa 100644
> --- a/include/net/bluetooth/hci_core.h
> +++ b/include/net/bluetooth/hci_core.h
> @@ -29,6 +29,7 @@
>  #include <linux/idr.h>
>  #include <linux/leds.h>
>  #include <linux/rculist.h>
> +#include <linux/spinlock.h>
>  
>  #include <net/bluetooth/hci.h>
>  #include <net/bluetooth/hci_drv.h>
> @@ -92,6 +93,7 @@ struct discovery_state {
>  	u16			uuid_count;
>  	u8			(*uuids)[16];
>  	unsigned long		name_resolve_timeout;
> +	spinlock_t		lock;
>  };
>  
>  #define SUSPEND_NOTIFIER_TIMEOUT	msecs_to_jiffies(2000) /* 2 seconds */
> @@ -878,6 +880,7 @@ static inline void iso_recv(struct hci_conn *hcon, struct sk_buff *skb,
>  
>  static inline void discovery_init(struct hci_dev *hdev)
>  {
> +	spin_lock_init(&hdev->discovery.lock);
>  	hdev->discovery.state = DISCOVERY_STOPPED;
>  	INIT_LIST_HEAD(&hdev->discovery.all);
>  	INIT_LIST_HEAD(&hdev->discovery.unknown);
> @@ -892,8 +895,11 @@ static inline void hci_discovery_filter_clear(struct hci_dev *hdev)
>  	hdev->discovery.report_invalid_rssi = true;
>  	hdev->discovery.rssi = HCI_RSSI_INVALID;
>  	hdev->discovery.uuid_count = 0;
> +
> +	spin_lock(&hdev->discovery.lock);
>  	kfree(hdev->discovery.uuids);
>  	hdev->discovery.uuids = NULL;
> +	spin_unlock(&hdev->discovery.lock);
>  }
>  
>  bool hci_discovery_active(struct hci_dev *hdev);