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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , John Heffner , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net] ipv4: Fix device use-after-free in ip_skb_dst_mtu() Message-ID: <20260928123411.GA440063@shredder> References: <20260927071051.3693368-1-nicoyip.dev@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260927071051.3693368-1-nicoyip.dev@gmail.com> X-ClientProxiedBy: FR0P281CA0013.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:15::18) To PH0PR12MB7957.namprd12.prod.outlook.com (2603:10b6:510:281::22) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR12MB7957:EE_|IA1PR12MB6185:EE_ X-MS-Office365-Filtering-Correlation-Id: 241bd679-f470-45a4-7c58-08df1d5cd226 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|23010399003|7416014|376014|10067099003|56012099006|3023799007|18002099003|22082099003|11063799006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?LQm8kJVyiuMnsGWI6Y9QvyFYpbyTFT5d3U6YQN6cTh7wtGxImVjOVWkpufRX?= =?us-ascii?Q?pgHcjVMpYsZhas+P2LDxVGQkVKtp1ydi5LZn2Uvr43h94XpolFuVCLFoebcY?= =?us-ascii?Q?KgpMRMz7spEMqVBy46keCjEYsVgfft/9cY4AMtp4AexbAhDv8kIK/QNgV14S?= =?us-ascii?Q?Jtp+r6i4aZdvRwbV6sPymKLYRUEsSx12Rx3Rm4Hdw1aa4MqBBImV8f+EQFMP?= =?us-ascii?Q?M9n4+NQN3tCvqcxLCrzq7KJa6L/2SND3FPeoGhsnPCVXKAJqG0CVnzkglgou?= =?us-ascii?Q?OG5x9aDvRVi0QPggVmDc7DLkYUIgwVbT1Y76wGE4RHkRUR2wlv1vjefHp0fi?= =?us-ascii?Q?8+3FIQh+6zCdDkkkDWnAbu18BVOJkgWYOzMotpuorgIqiEiuf1bbLj+0sp0X?= =?us-ascii?Q?1bKMBA01g5FVdEwmd+170aUPlG+b/X4w+s8B78h/zkN9dQiCIjY3oYxIh35j?= =?us-ascii?Q?Hg6N+wKt+UxN6ozRU1quBNPpFOekpY3+ga69J0mbNkK3K3o4VMCIUp3Fsm5C?= =?us-ascii?Q?Wb4iXoe/ac5VBFyAiZhWrN1YIGKUnyOEgPxTKmdVesXC+ZTW+zAGNxEG7zg5?= =?us-ascii?Q?CFQ3gEHbH+LH/QheIGHQjQmMN4iDKE3D8njRn93weQ9R8D/dBdyRTi+/qn1I?= =?us-ascii?Q?gWquTFFf1tEJafAfCf+VxY+hTK3rI6c2nmNjPVZkO3iHkxTkJQY2YAayvmEj?= =?us-ascii?Q?GMyXjvrfqwxfERRSYIqYXdvi9lXA90U1itL5alaibYkJFcBseROFyiSCyYhP?= =?us-ascii?Q?MzhkVfA0d1yICKs5N359bLlS3UmBFlDtuvjwzWS3N4YIQPAMiqx1C3Q/pFW+?= =?us-ascii?Q?5aXHsKo5sBKvlI2AfHY5X65app9juy6oxDSFZxkdv2bY+xRjTTiHVeVfZkin?= =?us-ascii?Q?XxtF5zPKFzi3d10UXINDHNozCsv14SfBZ/5Muu3q5QEDfozrsXyM2awfuxtK?= =?us-ascii?Q?gFUVHS5QvIngdLhssaKntJ/UmoYk2bvsb6w2AwRYcSa5fNL7NC99Tw+JHVGd?= =?us-ascii?Q?ClHnBueILRm/pJAaVjFAFBKapSjgmx8EmMr0jZro/tPIn7z7VN66ZzLRycbc?= =?us-ascii?Q?LHLSocIW7ZmTmxRSGDQ1rr4RtBHZIg/ECj/SBAEi8sUHgCdqQMW6GLOl9OUO?= =?us-ascii?Q?MTsRwyNdOP3bqJKJVlu31rcfpn/761Refc5atNxdIh3b4y5Y0t4esKhUSDnO?= =?us-ascii?Q?rqzwjwzzwOLEvV76js5uOIy8ef5VBBqZa7RHHMjCnvfjZjM7gYQRYR9xmv6q?= =?us-ascii?Q?MguGJhOQebsjUjj8vC+X6tH2sbdE117bAp/5GUJIK2cglLsoB86SNo1NMAmN?= =?us-ascii?Q?PlKLXeLlzi8E2oUWkpZllgVJkUdOKpETB/ATXOUltDIxVSjwDlGqA/Jm41EN?= =?us-ascii?Q?c9B+QOT8UxtIVCNsTwwiDCDmnY5d7qUZZ6Tewf8/dqoz9uatWYIxxB5S4fYi?= =?us-ascii?Q?ySIw4Vc5phIN356RgoocfnNMGM30Z4bwExlWTVsg9i9sr+Ak8ziFAVlkkNy9?= =?us-ascii?Q?9ehoLAFBEDZ+7HHlz0n3y6G+RuRHh5my2/gXSOeIiYz6Q051wG9kfyDJLIeP?= =?us-ascii?Q?PZwRTCxJN+Q7J2emEPHOMmCAW06VxGVsi04kXVLDco/H4hNO4PWOQa+A2EWA?= =?us-ascii?Q?qkXdFhDgmLX9aAOtLEZzWAwwAfFSnNubfxwv9LAMlpAEgfAVZUkz74tZxxSY?= =?us-ascii?Q?tZ335SMv6p9uA76Zz8tLjXKu+BSROhM+XVdqybR+fdYb0fsV?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 241bd679-f470-45a4-7c58-08df1d5cd226 X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB7957.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Sep 2026 12:34:21.2504 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: jzVpDb4Q+FEcKATPG+aXyi7uwy0EDS6MEtPtAQRKKAj6estfpbcSoBr309CbCl+Xo+7vst+zuninpJzt38RZDQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6185 On Sun, Sep 27, 2026 at 03:10:51PM +0800, Chengfeng Ye wrote: > When a socket ignores the path MTU, ip_skb_dst_mtu() reads the device > MTU without RCU protection. The multicast and broadcast output path > through ip_mc_output() can reach this helper without an RCU read lock. > Netfilter releases its internal read lock before calling > ip_finish_output(). > > A sender can load dst->dev and then be preempted before reading dev->mtu. > Concurrent device unregistration replaces dst->dev with blackhole_netdev > and drops the old device reference. After the grace period and remaining > references drain, the device can be freed before the sender resumes and > reads its MTU, causing a use-after-free. > > KASAN reported: > > BUG: KASAN: slab-use-after-free in ip_skb_dst_mtu+0x634/0x740 > Read of size 4 at addr ffff88810921c038 by task poc/98 > Call Trace: > ip_skb_dst_mtu+0x634/0x740 > __ip_finish_output.part.0+0x22/0x2c0 > ip_mc_output+0x287/0x930 > ip_send_skb+0x11d/0x150 > udp_send_skb+0x63e/0xdf0 > udp_sendmsg+0x1235/0x1da0 > __sys_sendto+0x32c/0x3a0 > > Allocated by task 97: > __kvmalloc_node_noprof+0x1d4/0x620 > alloc_netdev_mqs+0x81/0x12c0 > rtnl_create_link+0xaa3/0xe30 > rtnl_newlink+0xabc/0x1f70 > > Freed by task 99: > kfree+0x131/0x3c0 > device_release+0xc8/0x240 > kobject_put+0x14d/0x280 > netdev_run_todo+0x4cb/0xc70 > rtnl_dellink+0x362/0xa90 > > Protect the device lookup and MTU read with RCU and use dst_dev_rcu() to > access the device pointer. Keep the MTU limit and headroom calculation > unchanged. This still leaves other potential UAFs in the ip_mc_output() path. Better to fix it by adding an RCU read-side critical section in ip_mc_output() in a similar fashion to its unicast counterpart. See commit 1dbf1d590d10 ("net: Add locking to protect skb->dev access in ip_output"). You can blame 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()").