netdev - Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in __netlink_dump

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

Date: Sun, 9 Jun 2024 17:17:48 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Jiri Pirko <jiri@...nulli.us>, Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        netdev@...r.kernel.org, Ido Schimmel <idosch@...dia.com>,
        Jiri Pirko <jiri@...dia.com>, eric.dumazet@...il.com
Subject: Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in
 __netlink_dump_start()

Hello.

While investigating hung task reports involving rtnl_mutex, I came to
suspect that commit b5590270068c ("netlink: hold nlk->cb_mutex longer
in __netlink_dump_start()") is buggy, for that commit made only
mutex_lock(nlk->cb_mutex) side conditionally. Why don't we need to make
mutex_unlock(nlk->cb_mutex) side conditionally?

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index fa9c090cf629..c23a8d4ddcae 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2352,7 +2352,8 @@ static int netlink_dump(struct sock *sk, bool lock_taken)
 
 	if (nlk->dump_done_errno > 0 ||
 	    skb_tailroom(skb) < nlmsg_total_size(sizeof(nlk->dump_done_errno))) {
-		mutex_unlock(&nlk->nl_cb_mutex);
+		if (!lock_taken)
+			mutex_unlock(&nlk->nl_cb_mutex);
 
 		if (sk_filter(sk, skb))
 			kfree_skb(skb);
@@ -2386,13 +2387,15 @@ static int netlink_dump(struct sock *sk, bool lock_taken)
 	WRITE_ONCE(nlk->cb_running, false);
 	module = cb->module;
 	skb = cb->skb;
-	mutex_unlock(&nlk->nl_cb_mutex);
+	if (!lock_taken)
+		mutex_unlock(&nlk->nl_cb_mutex);
 	module_put(module);
 	consume_skb(skb);
 	return 0;
 
 errout_skb:
-	mutex_unlock(&nlk->nl_cb_mutex);
+	if (!lock_taken)
+		mutex_unlock(&nlk->nl_cb_mutex);
 	kfree_skb(skb);
 	return err;
 }