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

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Message-ID: <20240222105021.1943116-7-edumazet@google.com>
Date: Thu, 22 Feb 2024 10:50:13 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Ido Schimmel <idosch@...dia.com>, Jiri Pirko <jiri@...dia.com>, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in __netlink_dump_start()

__netlink_dump_start() releases nlk->cb_mutex right before
calling netlink_dump() which grabs it again.

This seems dangerous, even if KASAN did not bother yet.

Add a @lock_taken parameter to netlink_dump() to let it
grab the mutex if called from netlink_recvmsg() only.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/netlink/af_netlink.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 9c962347cf859f16fc76e4d8a2fd22cdb3d142d6..94f3860526bfaa5793e8b3917250ec0e751687b5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -130,7 +130,7 @@ static const char *const nlk_cb_mutex_key_strings[MAX_LINKS + 1] = {
 	"nlk_cb_mutex-MAX_LINKS"
 };
 
-static int netlink_dump(struct sock *sk);
+static int netlink_dump(struct sock *sk, bool lock_taken);
 
 /* nl_table locking explained:
  * Lookup and traversal are protected with an RCU read-side lock. Insertion
@@ -1987,7 +1987,7 @@ static int netlink_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
 	if (READ_ONCE(nlk->cb_running) &&
 	    atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) {
-		ret = netlink_dump(sk);
+		ret = netlink_dump(sk, false);
 		if (ret) {
 			WRITE_ONCE(sk->sk_err, -ret);
 			sk_error_report(sk);
@@ -2196,7 +2196,7 @@ static int netlink_dump_done(struct netlink_sock *nlk, struct sk_buff *skb,
 	return 0;
 }
 
-static int netlink_dump(struct sock *sk)
+static int netlink_dump(struct sock *sk, bool lock_taken)
 {
 	struct netlink_sock *nlk = nlk_sk(sk);
 	struct netlink_ext_ack extack = {};
@@ -2208,7 +2208,8 @@ static int netlink_dump(struct sock *sk)
 	int alloc_min_size;
 	int alloc_size;
 
-	mutex_lock(nlk->cb_mutex);
+	if (!lock_taken)
+		mutex_lock(nlk->cb_mutex);
 	if (!nlk->cb_running) {
 		err = -EINVAL;
 		goto errout_skb;
@@ -2365,9 +2366,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 	WRITE_ONCE(nlk->cb_running, true);
 	nlk->dump_done_errno = INT_MAX;
 
-	mutex_unlock(nlk->cb_mutex);
-
-	ret = netlink_dump(sk);
+	ret = netlink_dump(sk, true);
 
 	sock_put(sk);
 
-- 
2.44.0.rc1.240.g4c46232300-goog