netdev - [patch net-next] genetlink: hold read cb_lock during iteration of genl_fam_idr in genl

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Message-Id: <20220825081940.1283335-1-jiri@resnulli.us>
Date:   Thu, 25 Aug 2022 10:19:40 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, saeedm@...dia.com, jacob.e.keller@...el.com,
        vikas.gupta@...adcom.com, gospo@...adcom.com, fw@...len.de
Subject: [patch net-next] genetlink: hold read cb_lock during iteration of genl_fam_idr in genl_bind()

From: Jiri Pirko <jiri@...dia.com>

In genl_bind(), currently genl_lock and write cb_lock are taken
for iteration of genl_fam_idr and processing of static values
stored in struct genl_family. Take just read cb_lock for this task
as it is sufficient to guard the idr and the struct against
concurrent genl_register/unregister_family() calls.

This will allow to run genl command processing in genl_rcv() and
mnl_socket_setsockopt(.., NETLINK_ADD_MEMBERSHIP, ..) in parallel.

Reported-by: Vikas Gupta <vikas.gupta@...adcom.com>
Signed-off-by: Jiri Pirko <jiri@...dia.com>
---
 net/netlink/genetlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 57010927e20a..76aed0571e3a 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1362,7 +1362,7 @@ static int genl_bind(struct net *net, int group)
 	unsigned int id;
 	int ret = 0;
 
-	genl_lock_all();
+	down_read(&cb_lock);
 
 	idr_for_each_entry(&genl_fam_idr, family, id) {
 		const struct genl_multicast_group *grp;
@@ -1383,7 +1383,7 @@ static int genl_bind(struct net *net, int group)
 		break;
 	}
 
-	genl_unlock_all();
+	up_read(&cb_lock);
 	return ret;
 }
 
-- 
2.37.1