linux-kernel - [PATCH net v2] ipmr: Fix access to mfc_cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241108-ipmr_rcu-v2-1-c718998e209b@debian.org>
Date: Fri, 08 Nov 2024 06:08:36 -0800
From: Breno Leitao <leitao@...ian.org>
To: "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: David Ahern <dsahern@...il.com>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, kernel-team@...a.com, 
 Breno Leitao <leitao@...ian.org>
Subject: [PATCH net v2] ipmr: Fix access to mfc_cache_list without lock
 held

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@...ian.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(-)

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 &&

---
base-commit: 25d70702142ac2115e75e01a0a985c6ea1d78033
change-id: 20241107-ipmr_rcu-291d85400b16

Best regards,
-- 
Breno Leitao <leitao@...ian.org>