Subject: Re: [RESEND 1/1] Bluetooth: Use chan_list_lock to protect the whole put/destroy invokation

From: Lee Jones <[email-masked]>
Date: Mon, 27 Jun 2022 15:17:30 +0100

On Wed, 22 Jun 2022, Lee Jones wrote:

> This change prevents a use-after-free caused by one of the worker
> threads starting up (see below) *after* the final channel reference
> has been put() during sock_close() but *before* the references to the
> channel have been destroyed.
> 
>   refcount_t: increment on 0; use-after-free.
>   BUG: KASAN: use-after-free in refcount_dec_and_test+0x20/0xd0
>   Read of size 4 at addr ffffffc114f5bf18 by task kworker/u17:14/705
> 
>   CPU: 4 PID: 705 Comm: kworker/u17:14 Tainted: G S      W       4.14.234-00003-g1fb6d0bd49a4-dirty #28
>   Hardware name: Qualcomm Technologies, Inc. SM8150 V2 PM8150 Google Inc. MSM sm8150 Flame DVT (DT)
>   Workqueue: hci0 hci_rx_work
>   Call trace:
>    dump_backtrace+0x0/0x378
>    show_stack+0x20/0x2c
>    dump_stack+0x124/0x148
>    print_address_description+0x80/0x2e8
>    __kasan_report+0x168/0x188
>    kasan_report+0x10/0x18
>    __asan_load4+0x84/0x8c
>    refcount_dec_and_test+0x20/0xd0
>    l2cap_chan_put+0x48/0x12c
>    l2cap_recv_frame+0x4770/0x6550
>    l2cap_recv_acldata+0x44c/0x7a4
>    hci_acldata_packet+0x100/0x188
>    hci_rx_work+0x178/0x23c
>    process_one_work+0x35c/0x95c
>    worker_thread+0x4cc/0x960
>    kthread+0x1a8/0x1c4
>    ret_from_fork+0x10/0x18
> 
> Cc: [email-masked]
> Cc: Marcel Holtmann <[email-masked]>
> Cc: Johan Hedberg <[email-masked]>
> Cc: Luiz Augusto von Dentz <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Cc: Jakub Kicinski <[email-masked]>
> Cc: Paolo Abeni <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Lee Jones <[email-masked]>
> ---
>  net/bluetooth/l2cap_core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

This patch now passes all of the CI tests.

Except the check-patch/lint tests which return false positives.

Please consider for inclusion to remedy this serious bug.

TIA.

> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index ae78490ecd3d4..82279c5919fd8 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -483,9 +483,7 @@ static void l2cap_chan_destroy(struct kref *kref)
>  
>  	BT_DBG("chan %p", chan);
>  
> -	write_lock(&chan_list_lock);
>  	list_del(&chan->global_l);
> -	write_unlock(&chan_list_lock);
>  
>  	kfree(chan);
>  }
> @@ -501,7 +499,9 @@ void l2cap_chan_put(struct l2cap_chan *c)
>  {
>  	BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
>  
> +	write_lock(&chan_list_lock);
>  	kref_put(&c->kref, l2cap_chan_destroy);
> +	write_unlock(&chan_list_lock);
>  }
>  EXPORT_SYMBOL_GPL(l2cap_chan_put);
>  

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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