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Message-ID: <8dad5b42-a843-4935-a31e-91a2eadf0c72@collabora.com>
Date: Thu, 22 Feb 2024 11:23:05 +0000
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MIME-Version: 1.0
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Subject: Re: [PATCH v2] Bluetooth: af_bluetooth: Fix Use-After-Free in
 bt_sock_recvmsg
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To: Hyunwoo Kim <v4bel@theori.io>, marcel@holtmann.org, luiz.dentz@gmail.com
Cc: imv4bel@gmail.com, johan.hedberg@gmail.com,
 linux-bluetooth@vger.kernel.org
References: <20231209105518.GA408904@v4bel-B760M-AORUS-ELITE-AX>
From: Martyn Welch <martyn.welch@collabora.com>
In-Reply-To: <20231209105518.GA408904@v4bel-B760M-AORUS-ELITE-AX>
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Hi Hyunwoo,

I've been looking into a few CVEs, the one of interest in this case is 
CVE-2024-21803.

There seems to be little publicly available information about this CVE, 
however the title of this patch and the affected kernel range suggest 
this may be a fix for this CVE.

Would you be able to clarify whether this is a fix for CVE-2024-21803?

Thanks,

Martyn

On 09/12/2023 10:55, Hyunwoo Kim wrote:
> This can cause a race with bt_sock_ioctl() because
> bt_sock_recvmsg() gets the skb from sk->sk_receive_queue
> and then frees it without holding lock_sock.
> A use-after-free for a skb occurs with the following flow.
> ```
> bt_sock_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
> bt_sock_ioctl() -> skb_peek()
> ```
> Add lock_sock to bt_sock_recvmsg() to fix this issue.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
> ---
> v1 -> v2: Remove duplicate release_sock()s
> ---
>   net/bluetooth/af_bluetooth.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
> index 336a76165454..b93464ac3517 100644
> --- a/net/bluetooth/af_bluetooth.c
> +++ b/net/bluetooth/af_bluetooth.c
> @@ -309,11 +309,14 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>   	if (flags & MSG_OOB)
>   		return -EOPNOTSUPP;
>   
> +	lock_sock(sk);
> +
>   	skb = skb_recv_datagram(sk, flags, &err);
>   	if (!skb) {
>   		if (sk->sk_shutdown & RCV_SHUTDOWN)
> -			return 0;
> +			err = 0;
>   
> +		release_sock(sk);
>   		return err;
>   	}
>   
> @@ -343,6 +346,8 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>   
>   	skb_free_datagram(sk, skb);
>   
> +	release_sock(sk);
> +
>   	if (flags & MSG_TRUNC)
>   		copied = skblen;
>