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Wed, 17 Sep 2025 22:07:40 -0700 Date: Wed, 17 Sep 2025 22:07:38 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , Joerg Roedel , Kevin Tian , , Robin Murphy , Shuah Khan , Will Deacon , Lu Baolu , , Subject: Re: [PATCH 1/3] iommufd: Fix race during abort for file descriptors Message-ID: References: <0-v1-02cd136829df+31-iommufd_syz_fput_jgg@nvidia.com> <1-v1-02cd136829df+31-iommufd_syz_fput_jgg@nvidia.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1-v1-02cd136829df+31-iommufd_syz_fput_jgg@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF0000343B:EE_|CH3PR12MB8186:EE_ X-MS-Office365-Filtering-Correlation-Id: 818f5c02-647c-42a6-cdd7-08ddf6715337 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|36860700013|82310400026|13003099007; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Sep 2025 05:07:54.2883 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 818f5c02-647c-42a6-cdd7-08ddf6715337 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF0000343B.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8186 On Wed, Sep 17, 2025 at 05:01:47PM -0300, Jason Gunthorpe wrote: > Fix this by putting the core code in charge of the file lifetime, and call > __fput_sync() during abort to ensure that release() is called before > kfree. __fput_sync() is a bit too tricky to open code in all the object > implementations Mind elaborating this "too tricky"? I thought that we're supposed to use __fput_sync(), instead of fput(), in the alloc function in the first place? > Cc: stable@vger.kernel.org > Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object") > Reported-by: syzbot+80620e2d0d0a33b09f93@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/r/68c8583d.050a0220.2ff435.03a2.GAE@google.com > Signed-off-by: Jason Gunthorpe The patch looks good to me though: Reviewed-by: Nicolin Chen > @@ -131,10 +132,30 @@ void iommufd_object_abort(struct iommufd_ctx *ictx, struct iommufd_object *obj) > void iommufd_object_abort_and_destroy(struct iommufd_ctx *ictx, > struct iommufd_object *obj) > { > - if (iommufd_object_ops[obj->type].abort) > - iommufd_object_ops[obj->type].abort(obj); > + const struct iommufd_object_ops *ops = &iommufd_object_ops[obj->type]; > + > + if (ops->file_offset) { > + struct file **filep = ((void *)obj) + ops->file_offset; > + > + /* > + * files should hold a users refcount while the file is open and > + * put it back in their release. They should hold a pointer to > + * obj in their private data. Normal fput() is deferred to a Nit: there is only one file_offset per obj, so it should be "file" and "it/its"? > + * workqueue and can get out of order with the following > + * kfree(obj). Using the sync version ensures the release > + * happens immediately. During abort we require the file > + * refcount is one at this point - meaning the object alloc > + * function cannot do anything to allow another thread to take a > + * refcount prior to a guaranteed success. > + */ Thanks Nicolin