From: Breno Leitao leitao@debian.org
[ Upstream commit e28acc9c1ccfcb24c08e020828f69d0a915b06ae ]
Accessing `mr_table->mfc_cache_list` is protected by an RCU lock. In the following code flow, the RCU read lock is not held, causing the following error when `RCU_PROVE` is not held. The same problem might show up in the IPv6 code path.
6.12.0-rc5-kbuilder-01145-gbac17284bdcb #33 Tainted: G E N ----------------------------- net/ipv4/ipmr_base.c:313 RCU-list traversed in non-reader section!!
rcu_scheduler_active = 2, debug_locks = 1 2 locks held by RetransmitAggre/3519: #0: ffff88816188c6c0 (nlk_cb_mutex-ROUTE){+.+.}-{3:3}, at: __netlink_dump_start+0x8a/0x290 #1: ffffffff83fcf7a8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_dumpit+0x6b/0x90
stack backtrace: lockdep_rcu_suspicious mr_table_dump ipmr_rtm_dumproute rtnl_dump_all rtnl_dumpit netlink_dump __netlink_dump_start rtnetlink_rcv_msg netlink_rcv_skb netlink_unicast netlink_sendmsg
This is not a problem per see, since the RTNL lock is held here, so, it is safe to iterate in the list without the RCU read lock, as suggested by Eric.
To alleviate the concern, modify the code to use list_for_each_entry_rcu() with the RTNL-held argument.
The annotation will raise an error only if RTNL or RCU read lock are missing during iteration, signaling a legitimate problem, otherwise it will avoid this false positive.
This will solve the IPv6 case as well, since ip6mr_rtm_dumproute() calls this function as well.
Signed-off-by: Breno Leitao leitao@debian.org Reviewed-by: David Ahern dsahern@kernel.org Link: https://patch.msgid.link/20241108-ipmr_rcu-v2-1-c718998e209b@debian.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/ipmr_base.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/ipmr_base.c b/net/ipv4/ipmr_base.c index ea48bd15a575b..4a1a90a135406 100644 --- a/net/ipv4/ipmr_base.c +++ b/net/ipv4/ipmr_base.c @@ -301,7 +301,8 @@ int mr_table_dump(struct mr_table *mrt, struct sk_buff *skb, if (filter->filter_set) flags |= NLM_F_DUMP_FILTERED;
- list_for_each_entry_rcu(mfc, &mrt->mfc_cache_list, list) { + list_for_each_entry_rcu(mfc, &mrt->mfc_cache_list, list, + lockdep_rtnl_is_held()) { if (e < s_e) goto next_entry; if (filter->dev &&