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Date:   Tue, 2 May 2023 22:10:06 +0800
From:   Ruihan Li <lrh2000@pku.edu.cn>
To:     linux-bluetooth@vger.kernel.org
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Ruihan Li <lrh2000@pku.edu.cn>,
        syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] Bluetooth: Fix potential double free caused by
 hci_conn_unlink
Message-ID: <e3lpbuwudub45ymqoubloli7smktxhsgrrhz52ppmywei6dnbc@54tpwahrnrk6>
References: <20230430180535.168270-1-lrh2000@pku.edu.cn>
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On Mon, May 01, 2023 at 02:05:35AM +0800, Ruihan Li wrote:
> The hci_conn_unlink function is being called by hci_conn_del, which means
> it should not call hci_conn_del with the input parameter conn again. If it
> does, conn may have already been released when hci_conn_unlink returns,
> leading to potential UAF and double-free issues.
> 
> This patch resolves the problem by modifying hci_conn_unlink to release
> only conn's child links when necessary, but never release conn itself.

Syzbot also found this bug several days ago (but it does not email
linux-bluetooth until today).

Reported-by: syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=690b90b14f14f43f4688

> Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
> Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
> ---
> Changes since v1:
>  * CI complains that there are some merge conflicts. This is because
> 	void hci_conn_del(struct hci_conn *conn)
>    this completely unrelated line makes the patch dependent on another fix:
> 	https://lore.kernel.org/linux-bluetooth/20230430171847.156825-1-lrh2000@pku.edu.cn/
>    But actually, deleting that line makes the two patches independent of
>    each other, and everything still works.
> 
>  net/bluetooth/hci_conn.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index 85c34c837..5f388202f 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -1083,8 +1083,18 @@ static void hci_conn_unlink(struct hci_conn *conn)
>  	if (!conn->parent) {
>  		struct hci_link *link, *t;
>  
> -		list_for_each_entry_safe(link, t, &conn->link_list, list)
> -			hci_conn_unlink(link->conn);
> +		list_for_each_entry_safe(link, t, &conn->link_list, list) {
> +			struct hci_conn *child = link->conn;
> +
> +			hci_conn_unlink(child);
> +
> +			/* Due to race, SCO connection might be not established
> +			 * yet at this point. Delete it now, otherwise it is
> +			 * possible for it to be stuck and can't be deleted.
> +			 */
> +			if (child->handle == HCI_CONN_HANDLE_UNSET)
> +				hci_conn_del(child);
> +		}
>  
>  		return;
>  	}
> @@ -1100,12 +1110,5 @@ static void hci_conn_unlink(struct hci_conn *conn)
>  
>  	kfree(conn->link);
>  	conn->link = NULL;
> -
> -	/* Due to race, SCO connection might be not established
> -	 * yet at this point. Delete it now, otherwise it is
> -	 * possible for it to be stuck and can't be deleted.
> -	 */
> -	if (conn->handle == HCI_CONN_HANDLE_UNSET)
> -		hci_conn_del(conn);
>  }
>  
> -- 
> 2.40.0

Thanks,
Ruihan Li