From 6d4634d1b09172a9f5863d8c4cec8f82fbecdf15 Mon Sep 17 00:00:00 2001 From: Cambda Zhu Date: Tue, 8 Dec 2020 17:19:10 +0800 Subject: [PATCH] net: Limit logical shift left of TCP probe0 timeout For each TCP zero window probe, the icsk_backoff is increased by one and its max value is tcp_retries2. If tcp_retries2 is greater than 63, the probe0 timeout shift may exceed its max bits. On x86_64/ARMv8/MIPS, the shift count would be masked to range 0 to 63. And on ARMv7 the result is zero. If the shift count is masked, only several probes will be sent with timeout shorter than TCP_RTO_MAX. But if the timeout is zero, it needs tcp_retries2 times probes to end this false timeout. Besides, bitwise shift greater than or equal to the width is an undefined behavior. This patch adds a limit to the backoff. The max value of max_when is TCP_RTO_MAX and the min value of timeout base is TCP_RTO_MIN. The limit is the backoff from TCP_RTO_MIN to TCP_RTO_MAX. Signed-off-by: Cambda Zhu Link: https://lore.kernel.org/r/20201208091910.37618-1-cambda@linux.alibaba.com Signed-off-by: Jakub Kicinski --- include/net/tcp.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index b1a05f8b35f0c..78d13c88720fd 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1326,7 +1326,9 @@ static inline unsigned long tcp_probe0_base(const struct sock *sk) static inline unsigned long tcp_probe0_when(const struct sock *sk, unsigned long max_when) { - u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff; + u8 backoff = min_t(u8, ilog2(TCP_RTO_MAX / TCP_RTO_MIN) + 1, + inet_csk(sk)->icsk_backoff); + u64 when = (u64)tcp_probe0_base(sk) << backoff; return (unsigned long)min_t(u64, when, max_when); }