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-rw-r--r--include/net/tcp.h16
1 files changed, 13 insertions, 3 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7d734ba391fc..43e04e14c41e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -518,13 +518,23 @@ static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
reuse = rcu_dereference(sk->sk_reuseport_cb);
if (likely(reuse)) {
last_overflow = READ_ONCE(reuse->synq_overflow_ts);
- return time_after32(now, last_overflow +
- TCP_SYNCOOKIE_VALID);
+ return !time_between32(now, last_overflow - HZ,
+ last_overflow +
+ TCP_SYNCOOKIE_VALID);
}
}
last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
- return time_after32(now, last_overflow + TCP_SYNCOOKIE_VALID);
+
+ /* If last_overflow <= jiffies <= last_overflow + TCP_SYNCOOKIE_VALID,
+ * then we're under synflood. However, we have to use
+ * 'last_overflow - HZ' as lower bound. That's because a concurrent
+ * tcp_synq_overflow() could update .ts_recent_stamp after we read
+ * jiffies but before we store .ts_recent_stamp into last_overflow,
+ * which could lead to rejecting a valid syncookie.
+ */
+ return !time_between32(now, last_overflow - HZ,
+ last_overflow + TCP_SYNCOOKIE_VALID);
}
static inline u32 tcp_cookie_time(void)