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AJvYcCXIgAzb7W0eceRHVqQKGsA7cg1Zhm4Rck+JeZWbAFCq8gCZ6p3rsMy52obvTBX9/ieZVxbLGC8=@vger.kernel.org X-Gm-Message-State: AOJu0YzVTXPZEKDwObG5kqh4iTTJfTO03am0e1rrK6HYBcWE3zX3KU9A vWc3jTWszkVTUo5IxFfoob8M2HMnTwvGU0T5M9lqNHxx4w6ZujZcT3ECldi2nN6cIfW7pB6Grus SXLqppQ== X-Google-Smtp-Source: AGHT+IEQOeSykRo4Rj5MaMzLbvjbffFfTFsbM/EOLn0WBNXCeu8l+VNyetqRrDtzeRuqnAV/p+uqxvFuzh4= X-Received: from pjbsd7.prod.google.com ([2002:a17:90b:5147:b0:33b:b3b8:216b]) (user=kuniyu job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:5105:b0:32e:e3af:45f6 with SMTP id 98e67ed59e1d1-33bcf87b6a4mr33427079a91.10.1761263580523; Thu, 23 Oct 2025 16:53:00 -0700 (PDT) Date: Thu, 23 Oct 2025 23:52:38 +0000 In-Reply-To: <20251023191807.74006-2-stefan.wiehler@nokia.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251023191807.74006-2-stefan.wiehler@nokia.com> X-Mailer: git-send-email 2.51.1.851.g4ebd6896fd-goog Message-ID: <20251023235259.4179388-1-kuniyu@google.com> Subject: Re: [PATCH net] sctp: Hold RCU read lock while iterating over address list From: Kuniyuki Iwashima To: stefan.wiehler@nokia.com Cc: davem@davemloft.net, edumazet@google.com, horms@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-sctp@vger.kernel.org, lucien.xin@gmail.com, netdev@vger.kernel.org, pabeni@redhat.com, kuniyu@google.com Content-Type: text/plain; charset="UTF-8" From: Stefan Wiehler Date: Thu, 23 Oct 2025 21:18:08 +0200 > With CONFIG_PROVE_RCU_LIST=y and by executing > > $ netcat -l --sctp & > $ netcat --sctp localhost & > $ ss --sctp > > one can trigger the following Lockdep-RCU splat(s): > > WARNING: suspicious RCU usage > 6.18.0-rc1-00093-g7f864458e9a6 #5 Not tainted > ----------------------------- > net/sctp/diag.c:76 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 2 locks held by ss/215: > #0: ffff9c740828bec0 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{4:4}, at: __netlink_dump_start+0x84/0x2b0 > #1: ffff9c7401d72cd0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: sctp_sock_dump+0x38/0x200 > > stack backtrace: > CPU: 0 UID: 0 PID: 215 Comm: ss Not tainted 6.18.0-rc1-00093-g7f864458e9a6 #5 PREEMPT(voluntary) > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > Call Trace: > > dump_stack_lvl+0x5d/0x90 > lockdep_rcu_suspicious.cold+0x4e/0xa3 > inet_sctp_diag_fill.isra.0+0x4b1/0x5d0 > sctp_sock_dump+0x131/0x200 > sctp_transport_traverse_process+0x170/0x1b0 > ? __pfx_sctp_sock_filter+0x10/0x10 > ? __pfx_sctp_sock_dump+0x10/0x10 > sctp_diag_dump+0x103/0x140 > __inet_diag_dump+0x70/0xb0 > netlink_dump+0x148/0x490 > __netlink_dump_start+0x1f3/0x2b0 > inet_diag_handler_cmd+0xcd/0x100 > ? __pfx_inet_diag_dump_start+0x10/0x10 > ? __pfx_inet_diag_dump+0x10/0x10 > ? __pfx_inet_diag_dump_done+0x10/0x10 > sock_diag_rcv_msg+0x18e/0x320 > ? __pfx_sock_diag_rcv_msg+0x10/0x10 > netlink_rcv_skb+0x4d/0x100 > netlink_unicast+0x1d7/0x2b0 > netlink_sendmsg+0x203/0x450 > ____sys_sendmsg+0x30c/0x340 > ___sys_sendmsg+0x94/0xf0 > __sys_sendmsg+0x83/0xf0 > do_syscall_64+0xbb/0x390 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > ... > > > Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file") > Signed-off-by: Stefan Wiehler > --- > It might be sufficient to add a check for one of the already held locks, > but I lack the domain knowledge to be sure about that... > --- > net/sctp/diag.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/sctp/diag.c b/net/sctp/diag.c > index 996c2018f0e6..1a8761f87bf1 100644 > --- a/net/sctp/diag.c > +++ b/net/sctp/diag.c > @@ -73,19 +73,23 @@ static int inet_diag_msg_sctpladdrs_fill(struct sk_buff *skb, > struct nlattr *attr; > void *info = NULL; > > + rcu_read_lock(); > list_for_each_entry_rcu(laddr, address_list, list) > addrcnt++; > + rcu_read_unlock(); > > attr = nla_reserve(skb, INET_DIAG_LOCALS, addrlen * addrcnt); > if (!attr) > return -EMSGSIZE; > > info = nla_data(attr); > + rcu_read_lock(); > list_for_each_entry_rcu(laddr, address_list, list) { > memcpy(info, &laddr->a, sizeof(laddr->a)); > memset(info + sizeof(laddr->a), 0, addrlen - sizeof(laddr->a)); > info += addrlen; looks like TOCTOU issue exists here, we should check the boundary like this: if (!--addrcnt) break; Otherwise KASAN would complain about an out-of-bound write. > } > + rcu_read_unlock(); > > return 0; > } > -- > 2.51.0