Patch "net: Fix data-races around sysctl_max_skb_frags." has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    net: Fix data-races around sysctl_max_skb_frags.

to the 5.15-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:
     net-fix-data-races-around-sysctl_max_skb_frags.patch
and it can be found in the queue-5.15 subdirectory.

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



commit b5d6159813c34a4e0fc2b00195c6f768bc78bb27
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Tue Aug 23 10:46:54 2022 -0700

    net: Fix data-races around sysctl_max_skb_frags.
    
    [ Upstream commit 657b991afb89d25fe6c4783b1b75a8ad4563670d ]
    
    While reading sysctl_max_skb_frags, it can be changed concurrently.
    Thus, we need to add READ_ONCE() to its readers.
    
    Fixes: 5f74f82ea34c ("net:Add sysctl_max_skb_frags")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 52f51717f02f3..0ebef2a5950cd 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -991,7 +991,7 @@ struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags,
 
 	i = skb_shinfo(skb)->nr_frags;
 	can_coalesce = skb_can_coalesce(skb, i, page, offset);
-	if (!can_coalesce && i >= sysctl_max_skb_frags) {
+	if (!can_coalesce && i >= READ_ONCE(sysctl_max_skb_frags)) {
 		tcp_mark_push(tp, skb);
 		goto new_segment;
 	}
@@ -1344,7 +1344,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 			if (!skb_can_coalesce(skb, i, pfrag->page,
 					      pfrag->offset)) {
-				if (i >= sysctl_max_skb_frags) {
+				if (i >= READ_ONCE(sysctl_max_skb_frags)) {
 					tcp_mark_push(tp, skb);
 					goto new_segment;
 				}
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a089791414bfb..5df60a4b09304 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1317,7 +1317,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 
 		i = skb_shinfo(skb)->nr_frags;
 		can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
-		if (!can_coalesce && i >= sysctl_max_skb_frags) {
+		if (!can_coalesce && i >= READ_ONCE(sysctl_max_skb_frags)) {
 			tcp_mark_push(tcp_sk(ssk), skb);
 			goto alloc_skb;
 		}