[PATCH v2 net 11/17] net: Fix data-races around sysctl_max_skb_frags.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

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@amazon.com>
---
CC: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>
---
 net/ipv4/tcp.c       | 4 ++--
 net/mptcp/protocol.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 970e9a2cca4a..9a6fe3d6ab26 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1000,7 +1000,7 @@ static 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;
 	}
@@ -1354,7 +1354,7 @@ 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 da4257504fad..d398f3810662 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1263,7 +1263,7 @@ 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;
 		}
-- 
2.30.2