From 38f50242bf0f237cdc262308d624d333286ec3c5 Mon Sep 17 00:00:00 2001 From: Stefan Wiehler Date: Tue, 28 Oct 2025 17:12:26 +0100 Subject: sctp: Hold RCU read lock while iterating over address list 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 Reviewed-by: Kuniyuki Iwashima Acked-by: Xin Long Link: https://patch.msgid.link/20251028161506.3294376-2-stefan.wiehler@nokia.com Signed-off-by: Jakub Kicinski --- net/sctp/diag.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'net/sctp/diag.c') 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; } + rcu_read_unlock(); return 0; } -- cgit v1.2.3 From 95aef86ab231f047bb8085c70666059b58f53c09 Mon Sep 17 00:00:00 2001 From: Stefan Wiehler Date: Tue, 28 Oct 2025 17:12:27 +0100 Subject: sctp: Prevent TOCTOU out-of-bounds write For the following path not holding the sock lock, sctp_diag_dump() -> sctp_for_each_endpoint() -> sctp_ep_dump() make sure not to exceed bounds in case the address list has grown between buffer allocation (time-of-check) and write (time-of-use). Suggested-by: Kuniyuki Iwashima Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file") Signed-off-by: Stefan Wiehler Reviewed-by: Kuniyuki Iwashima Acked-by: Xin Long Link: https://patch.msgid.link/20251028161506.3294376-3-stefan.wiehler@nokia.com Signed-off-by: Jakub Kicinski --- net/sctp/diag.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'net/sctp/diag.c') diff --git a/net/sctp/diag.c b/net/sctp/diag.c index 1a8761f87bf1..5d64dd99ca9a 100644 --- a/net/sctp/diag.c +++ b/net/sctp/diag.c @@ -88,6 +88,9 @@ static int inet_diag_msg_sctpladdrs_fill(struct sk_buff *skb, memcpy(info, &laddr->a, sizeof(laddr->a)); memset(info + sizeof(laddr->a), 0, addrlen - sizeof(laddr->a)); info += addrlen; + + if (!--addrcnt) + break; } rcu_read_unlock(); -- cgit v1.2.3 From f1fc201148c7e684c10a72b6a3375597f28d1ef6 Mon Sep 17 00:00:00 2001 From: Stefan Wiehler Date: Tue, 28 Oct 2025 17:12:28 +0100 Subject: sctp: Hold sock lock while iterating over address list Move address list traversal in inet_assoc_attr_size() under the sock lock to avoid holding the RCU read lock. Suggested-by: Xin Long Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file") Signed-off-by: Stefan Wiehler Acked-by: Xin Long Link: https://patch.msgid.link/20251028161506.3294376-4-stefan.wiehler@nokia.com Signed-off-by: Jakub Kicinski --- net/sctp/diag.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) (limited to 'net/sctp/diag.c') diff --git a/net/sctp/diag.c b/net/sctp/diag.c index 5d64dd99ca9a..2afb376299fe 100644 --- a/net/sctp/diag.c +++ b/net/sctp/diag.c @@ -230,14 +230,15 @@ struct sctp_comm_param { bool net_admin; }; -static size_t inet_assoc_attr_size(struct sctp_association *asoc) +static size_t inet_assoc_attr_size(struct sock *sk, + struct sctp_association *asoc) { int addrlen = sizeof(struct sockaddr_storage); int addrcnt = 0; struct sctp_sockaddr_entry *laddr; list_for_each_entry_rcu(laddr, &asoc->base.bind_addr.address_list, - list) + list, lockdep_sock_is_held(sk)) addrcnt++; return nla_total_size(sizeof(struct sctp_info)) @@ -263,11 +264,14 @@ static int sctp_sock_dump_one(struct sctp_endpoint *ep, struct sctp_transport *t if (err) return err; - rep = nlmsg_new(inet_assoc_attr_size(assoc), GFP_KERNEL); - if (!rep) + lock_sock(sk); + + rep = nlmsg_new(inet_assoc_attr_size(sk, assoc), GFP_KERNEL); + if (!rep) { + release_sock(sk); return -ENOMEM; + } - lock_sock(sk); if (ep != assoc->ep) { err = -EAGAIN; goto out; -- cgit v1.2.3