From be265eef0631217e6566781d388ae078c4797752 Mon Sep 17 00:00:00 2001
From: Stefano Brivio <sbrivio@redhat.com>
Date: Wed, 26 Jan 2022 06:45:31 +0100
Subject: tcp: Don't round down MSS to >= 64KiB page size, but clamp it in any
case
On some architectures, the page size is bigger than the maximum size
of an Ethernet frame.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
tcp.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/tcp.c b/tcp.c
index 18f07b6..36c2bb5 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1671,7 +1671,7 @@ static int tcp_send_to_tap(struct ctx *c, struct tcp_tap_conn *conn, int flags,
}
if (flags & SYN) {
- uint16_t mss;
+ int mss;
/* Options: MSS, NOP and window scale (8 bytes) */
optlen = OPT_MSS_LEN + 1 + OPT_WS_LEN;
@@ -1691,10 +1691,10 @@ static int tcp_send_to_tap(struct ctx *c, struct tcp_tap_conn *conn, int flags,
if (c->low_wmem &&
!conn->local && !tcp_rtt_dst_low(conn))
mss = MIN(mss, PAGE_SIZE);
- else
+ else if (mss > PAGE_SIZE)
mss = ROUND_DOWN(mss, PAGE_SIZE);
}
- *(uint16_t *)data = htons(mss);
+ *(uint16_t *)data = htons(MIN(USHRT_MAX, mss));
data += OPT_MSS_LEN - 2;
th->doff += OPT_MSS_LEN / 4;
--
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