Patch "netlink: hold nlk->cb_mutex longer in __netlink_dump_start()" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    netlink: hold nlk->cb_mutex longer in __netlink_dump_start()

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netlink-hold-nlk-cb_mutex-longer-in-__netlink_dump_s.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a2766b7d702cc381932bb1e2ce223affe1e1ce36
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Thu Feb 22 10:50:13 2024 +0000

    netlink: hold nlk->cb_mutex longer in __netlink_dump_start()
    
    [ Upstream commit b5590270068c4324dac4a2b5a4a156e02e21339f ]
    
    __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@xxxxxxxxxx>
    Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ac3678d2d6d52..4f2a3d46554ff 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -126,7 +126,7 @@ 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
@@ -1996,7 +1996,7 @@ 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) {
 			sk->sk_err = -ret;
 			sk->sk_error_report(sk);
@@ -2206,7 +2206,7 @@ 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 = {};
@@ -2218,7 +2218,8 @@ 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;
@@ -2374,9 +2375,7 @@ 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);