| Message ID | 20241108-ipmr_rcu-v2-1-c718998e209b@debian.org (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net,v2] ipmr: Fix access to mfc_cache_list without lock held | expand |
diff --git a/net/ipv4/ipmr_base.c b/net/ipv4/ipmr_base.c index 271dc03fc6dbd9b35db4d5782716679134f225e4..f0af12a2f70bcdf5ba54321bf7ebebe798318abb 100644 --- a/net/ipv4/ipmr_base.c +++ b/net/ipv4/ipmr_base.c @@ -310,7 +310,8 @@ 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 &&
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> --- Changes in v2: - Instead of getting an RCU read lock, rely on rtnl mutex (Eric) - Link to v1: https://lore.kernel.org/r/20241107-ipmr_rcu-v1-1-ad0cba8dffed@debian.org - Still sending it against `net`, so, since this warning is annoying --- net/ipv4/ipmr_base.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- base-commit: 25d70702142ac2115e75e01a0a985c6ea1d78033 change-id: 20241107-ipmr_rcu-291d85400b16 Best regards,