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Wed, 23 Jun 2021 11:41:06 +0000 Subject: Re: [PATCH] ovl: fix mmap denywrite To: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org, linux-mm , Chengguang Xu , overlayfs References: From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <8d9ac67c-8e97-3f53-95b8-548a8bec6358@amd.com> Date: Wed, 23 Jun 2021 13:41:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [2a02:908:1252:fb60:69e4:a619:aa86:4e9c] X-ClientProxiedBy: PR3P191CA0056.EURP191.PROD.OUTLOOK.COM (2603:10a6:102:55::31) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:69e4:a619:aa86:4e9c] (2a02:908:1252:fb60:69e4:a619:aa86:4e9c) by PR3P191CA0056.EURP191.PROD.OUTLOOK.COM (2603:10a6:102:55::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4242.19 via Frontend Transport; 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Similarly negative i_mmap_writable counts were ignored for >>> VM_SHARED mappings. >>> >>> Fix by making vma_set_file() switch the temporary counts obtained and >>> released by mmap_region(). >> Mhm, I don't fully understand the background but that looks like >> something specific to overlayfs to me. >> >> So why are you changing the common helper? > Need to hold the temporary counts until the final ones are obtained in > vma_link(), which is out of overlayfs' scope. Ah! So basically we need to move the denial counts which mmap_region() added to the original file to the new one as well. That's indeed a rather good point. Can you rather change the vma_set_file() function to return the error and add a __must_check? I can take care fixing the users in DMA-buf and DRM subsystem. Thanks, Christian. > > Thanks, > Miklos