linux-kernel - Re: [PATCH] net: qrtr: Avoid potential use after free in MHI send

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Date:   Thu, 22 Apr 2021 09:56:04 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: qrtr: Avoid potential use after free in MHI send

On Wed, Apr 21, 2021 at 10:40:07AM -0700, Bjorn Andersson wrote:
> It is possible that the MHI ul_callback will be invoked immediately
> following the queueing of the skb for transmission, leading to the
> callback decrementing the refcount of the associated sk and freeing the
> skb.
> 
> As such the dereference of skb and the increment of the sk refcount must
> happen before the skb is queued, to avoid the skb to be used after free
> and potentially the sk to drop its last refcount..
> 
> Fixes: 6e728f321393 ("net: qrtr: Add MHI transport layer")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Thanks,
Mani

> ---
>  net/qrtr/mhi.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/qrtr/mhi.c b/net/qrtr/mhi.c
> index 2bf2b1943e61..fa611678af05 100644
> --- a/net/qrtr/mhi.c
> +++ b/net/qrtr/mhi.c
> @@ -50,6 +50,9 @@ static int qcom_mhi_qrtr_send(struct qrtr_endpoint *ep, struct sk_buff *skb)
>  	struct qrtr_mhi_dev *qdev = container_of(ep, struct qrtr_mhi_dev, ep);
>  	int rc;
>  
> +	if (skb->sk)
> +		sock_hold(skb->sk);
> +
>  	rc = skb_linearize(skb);
>  	if (rc)
>  		goto free_skb;
> @@ -59,12 +62,11 @@ static int qcom_mhi_qrtr_send(struct qrtr_endpoint *ep, struct sk_buff *skb)
>  	if (rc)
>  		goto free_skb;
>  
> -	if (skb->sk)
> -		sock_hold(skb->sk);
> -
>  	return rc;
>  
>  free_skb:
> +	if (skb->sk)
> +		sock_put(skb->sk);
>  	kfree_skb(skb);
>  
>  	return rc;
> -- 
> 2.29.2
>