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Thu, 21 May 2020 21:57:33 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userp3030.oracle.com with ESMTP id 314gma0g5p-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 21 May 2020 21:57:33 +0000 Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 04LLvUUl029917; Thu, 21 May 2020 21:57:31 GMT Received: from [10.39.200.114] (/10.39.200.114) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 21 May 2020 14:57:29 -0700 Subject: Re: [PATCH] xen/events: avoid NULL pointer dereference in evtchn_from_irq() To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: Juergen Gross , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Stefano Stabellini , stable@vger.kernel.org References: <20200319071428.12115-1-jgross@suse.com> <30719c35-6de7-d400-7bb8-cff4570f8971@oracle.com> <20200521184602.GP98582@mail-itl> From: Boris Ostrovsky Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200521184602.GP98582@mail-itl> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9628 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 mlxlogscore=999 adultscore=0 phishscore=0 mlxscore=0 spamscore=0 suspectscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005210162 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9628 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 mlxscore=0 cotscore=-2147483648 impostorscore=0 malwarescore=0 mlxlogscore=999 lowpriorityscore=0 phishscore=0 spamscore=0 bulkscore=0 adultscore=0 priorityscore=1501 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005210162 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/21/20 2:46 PM, Marek Marczykowski-Górecki wrote: > On Thu, May 21, 2020 at 01:22:03PM -0400, Boris Ostrovsky wrote: >> On 3/19/20 3:14 AM, Juergen Gross wrote: >>> There have been reports of races in evtchn_from_irq() where the info >>> pointer has been NULL. >>> >>> Avoid that case by testing info before dereferencing it. >>> >>> In order to avoid accessing a just freed info structure do the kfree() >>> via kfree_rcu(). >> >> Looks like noone ever responded to this. >> >> >> This change looks fine but is there a background on the problem? I >> looked in the archives and didn't find the relevant discussion. > Here is the original bug report: > https://xen.markmail.org/thread/44apwkwzeme4uavo > Thanks. Do we know what the race is? Is it because an event is being delivered from a dying guest who is in the process of tearing down event channels? -boris