linux-kernel - Re: [PATCH v1 2/8] bus: mhi: core: Add range check for channel id received in event ring

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Message-ID: <a96fe386-e27c-79b8-0315-1b974c998d40@codeaurora.org>
Date:   Mon, 27 Apr 2020 18:28:37 -0700
From:   Hemant Kumar <hemantk@...eaurora.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Bhaumik Bhatt <bbhatt@...eaurora.org>, mani@...nel.org
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/8] bus: mhi: core: Add range check for channel id
 received in event ring



On 4/27/20 11:50 AM, Jeffrey Hugo wrote:
> On 4/27/2020 12:32 PM, Bhaumik Bhatt wrote:
>> From: Hemant Kumar <hemantk@...eaurora.org>
>>
>> MHI data completion handler function reads channel id from event
>> ring element. Value is under the control of MHI devices and can be
>> any value between 0 and 255. In order to prevent out of bound access
>> add a bound check against the max channel supported by controller
>> and skip processing of that event ring element.
>>
>> Signed-off-by: Hemant Kumar <hemantk@...eaurora.org>
> 
> I believe your SOB is needed here after Hemant's per section 11 of 
> Documentation/process/submitting-patches.rst
> 
>> ---
>>   drivers/bus/mhi/core/main.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>> index 23154f1..ba8afa7 100644
>> --- a/drivers/bus/mhi/core/main.c
>> +++ b/drivers/bus/mhi/core/main.c
>> @@ -827,6 +827,9 @@ int mhi_process_data_event_ring(struct 
>> mhi_controller *mhi_cntrl,
>>           enum mhi_pkt_type type = MHI_TRE_GET_EV_TYPE(local_rp);
>>           chan = MHI_TRE_GET_EV_CHID(local_rp);
>> +        if (WARN_ON(chan >= mhi_cntrl->max_chan))
>> +            continue;
>> +
>>           mhi_chan = &mhi_cntrl->mhi_chan[chan];
>>           if (likely(type == MHI_PKT_TYPE_TX_EVENT)) {
>>
> 
> How does this work?
> 
> I understand the need for the range check, however I looks like this 
> change doesn't do proper handling.
> 
> Since all you do is "continue", we'll remain stuck in the while loop 
> this exists in, continuously "processing" the same event, failing the 
> same check, and spamming the kernel log with the WARN_ON output until 
> the end of time.
> 
> What am I missing?
Idea was to drop the event and continue, but continue statement is 
wrong here, we need to recycle the event and continue after that. Will 
fix in V2.
> 
> What is the behavior you want?  Do you want to just drop/ignore the 
> invalid event, or issue a reset of the device because it is clearly 
> misbehaving?
> 

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