From be265eef0631217e6566781d388ae078c4797752 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Wed, 26 Jan 2022 06:45:31 +0100 Subject: [PATCH] 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 --- 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;