[PATCH 6.4 694/800] tcp: annotate data races in __tcp_oow_rate_limited()

Greg Kroah-Hartman
2023-07-16T20:26:41Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 998127cdb4699b9d470a9348ffe9f1154346be5f ]

request sockets are lockless, __tcp_oow_rate_limited() could be called
on the same object from different cpus. This is harmless.

Add READ_ONCE()/WRITE_ONCE() annotations to avoid a KCSAN report.

Fixes: 4ce7e93cb3fe ("tcp: rate limit ACK sent by SYN_RECV request sockets")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/tcp_input.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bf8b22218dd46..57f1e4883b761 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3590,8 +3590,11 @@ static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32
static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
u32 *last_oow_ack_time)
{
- if (*last_oow_ack_time) {
- s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
+ /* Paired with the WRITE_ONCE() in this function. */
+ u32 val = READ_ONCE(*last_oow_ack_time);
+
+ if (val) {
+ s32 elapsed = (s32)(tcp_jiffies32 - val);

if (0 <= elapsed &&
elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
@@ -3600,7 +3603,10 @@ static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
}
}

- *last_oow_ack_time = tcp_jiffies32;
+ /* Paired with the prior READ_ONCE() and with itself,
+ * as we might be lockless.
+ */
+ WRITE_ONCE(*last_oow_ack_time, tcp_jiffies32);

return false; /* not rate-limited: go ahead, send dupack now! */
}
--
2.39.2