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Subject: Re: [PATCH 064/190] Revert "nfc: s3fwrn5: replace the assertion with
 a WARN_ON"
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     Aditya Pakki <pakki001@umn.edu>,
        "David S . Miller" <davem@davemloft.net>
References: <20210421130105.1226686-1-gregkh@linuxfoundation.org>
 <20210421130105.1226686-65-gregkh@linuxfoundation.org>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Message-ID: <9c2877c3-8077-c2e2-ed0d-80b2a0c87634@canonical.com>
Date:   Fri, 23 Apr 2021 09:29:57 +0200
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On 21/04/2021 14:58, Greg Kroah-Hartman wrote:
> This reverts commit 615f22f58029aa747b12768985e7f91cd053daa2.
> 
> Commits from @umn.edu addresses have been found to be submitted in "bad
> faith" to try to test the kernel community's ability to review "known
> malicious" changes.  The result of these submissions can be found in a
> paper published at the 42nd IEEE Symposium on Security and Privacy
> entitled, "Open Source Insecurity: Stealthily Introducing
> Vulnerabilities via Hypocrite Commits" written by Qiushi Wu (University
> of Minnesota) and Kangjie Lu (University of Minnesota).
> 
> Because of this, all submissions from this group must be reverted from
> the kernel tree and will need to be re-reviewed again to determine if
> they actually are a valid fix.  Until that work is complete, remove this
> change to ensure that no problems are being introduced into the
> codebase.
> 
> Cc: Aditya Pakki <pakki001@umn.edu>
> Cc: David S. Miller <davem@davemloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/nfc/s3fwrn5/firmware.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/nfc/s3fwrn5/firmware.c b/drivers/nfc/s3fwrn5/firmware.c
> index eb5d7a5beac7..f77f183c9bd0 100644
> --- a/drivers/nfc/s3fwrn5/firmware.c
> +++ b/drivers/nfc/s3fwrn5/firmware.c
> @@ -492,10 +492,7 @@ int s3fwrn5_fw_recv_frame(struct nci_dev *ndev, struct sk_buff *skb)
>  	struct s3fwrn5_info *info = nci_get_drvdata(ndev);
>  	struct s3fwrn5_fw_info *fw_info = &info->fw_info;
>  
> -	if (WARN_ON(fw_info->rsp)) {
> -		kfree_skb(skb);
> -		return -EINVAL;
> -	}
> +	BUG_ON(fw_info->rsp);

It took me some time to understand this but the original commit looks
correct. The recv_frame functions s3fwrn5_recv_frame() or
nci_recv_frame() should free the skb buffer on errors.  Here, the
s3fwrn5_fw_recv_frame() should be called only after sending a FW msg and
is expected to have fw_info->rsp=NULL. Otherwise it could mean that
frame came twice or it came when we did not ask for it.

Original code looks good, please drop the revert.

Best regards,
Krzysztof