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Ivanov" Cc: dsahern@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, kuniyu@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+84d4a405ed798b40c96d@syzkaller.appspotmail.com Subject: Re: [PATCH net] ipv6: Change allocation flags to match rcu_read_lock section requirements Message-ID: <20260719125507.GA2005035@shredder> References: <20260719105759.558050-1-zlatistiv@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260719105759.558050-1-zlatistiv@gmail.com> X-ClientProxiedBy: FR0P281CA0144.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:96::19) To SA3PR12MB7901.namprd12.prod.outlook.com (2603:10b6:806:306::12) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA3PR12MB7901:EE_|CH1PR12MB9670:EE_ X-MS-Office365-Filtering-Correlation-Id: 80a2c2f8-424d-48b4-bfad-08dee594fb5f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|23010399003|1800799024|6133799003|22082099003|18002099003|56012099006|11063799006|10067099003; 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Ivanov wrote: > Since the call to __ip6_del_rt_siblings has been converted under > rcu read lock and it only has one call point > we should no longer block or yield. > > Our stack trace from the syzbot reproducer looks as follows: > > __ip6_del_rt_siblings > rtnl_notify (Here we pass gfp_any() -> GFP_KERNEL) > nlmsg_notify > nlmsg_multicast > nlmsg_multicast_filtered > netlink_broadcast_filtered (GFP_KERNEL passed from earlier) > > netlink_broadcast_filtered can yield if GFP_KERNEL > is passed, which we do not want to happen. > > Fix this by changing the allocation flag of rtnl_notify. > > Also change the flag passed to nlmsg_new. Even though it > is not related to the syzbot generated bug it still falls > under the same requirements. I believe that the nlmsg_new() change is a no-op given that gfp_any() evaluates to GFP_ATOMIC under spin_lock_bh(), but it makes __ip6_del_rt_siblings() consistent with inet6_rt_notify() which already uses GFP_ATOMIC for both nlmsg_new() and rtnl_notify(). > > Reported-by: syzbot+84d4a405ed798b40c96d@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=84d4a405ed798b40c96d > Fixes: bd11ff421d36 ("ipv6: Get rid of RTNL for SIOCDELRT and RTM_DELROUTE.") > Signed-off-by: Nikola Z. Ivanov Reviewed-by: Ido Schimmel