[PATCH] net: qrtr: Avoid potential use after free in MHI send

[PATCH] net: qrtr: Avoid potential use after free in MHI send

[Bjorn Andersson]

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@linaro.org>
---
 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

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed, 21 Apr 2021 10:40:07 -0700 you 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..
> 
> [...]

Here is the summary with links:
  - net: qrtr: Avoid potential use after free in MHI send
    https://git.kernel.org/netdev/net/c/47a017f33943

You are awesome, thank you!
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https://korg.docs.kernel.org/patchwork/pwbot.html

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

[Manivannan Sadhasivam]

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@linaro.org>

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

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

[patchwork-bot+linux-arm-msm]

Hello:

This patch was applied to qcom/linux.git (refs/heads/for-next):

On Wed, 21 Apr 2021 10:40:07 -0700 you 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..
> 
> [...]

Here is the summary with links:
  - net: qrtr: Avoid potential use after free in MHI send
    https://git.kernel.org/qcom/c/47a017f33943

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html