linux-kernel - Re: [PATCH][next] drm/dp_mst: fix multiple frees of tx->bytes

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Date:   Wed, 20 Nov 2019 19:11:03 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Lyude Paul <lyude@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drm/dp_mst: fix multiple frees of tx->bytes

On 20/11/2019 18:59, Lyude Paul wrote:
> Heh, surprised I missed this one!
> 
> Reviewed-by: Lyude Paul <lyude@...hat.com>
> 
> Do you need me to push this to drm-misc, or do you have commit rights already

I have no commit rights.


> 
> On Wed, 2019-11-20 at 17:35 +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> Currently tx->bytes is being freed r->num_transactions number of
>> times because tx is not being set correctly. Fix this by setting
>> tx to &r->transactions[i] so that the correct objects are being
>> freed on each loop iteration.
>>
>> Addresses-Coverity: ("Double free")
>> Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
>> selftests")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  drivers/gpu/drm/drm_dp_mst_topology.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
>> b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index ae5809a1f19a..2754e7e075e7 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -517,8 +517,10 @@ drm_dp_decode_sideband_req(const struct
>> drm_dp_sideband_msg_tx *raw,
>>  			}
>>  
>>  			if (failed) {
>> -				for (i = 0; i < r->num_transactions; i++)
>> +				for (i = 0; i < r->num_transactions; i++) {
>> +					tx = &r->transactions[i];
>>  					kfree(tx->bytes);
>> +				}
>>  				return -ENOMEM;
>>  			}
>>