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tcp: Don't round down MSS to >= 64KiB page size, but clamp it in any case

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On some architectures, the page size is bigger than the maximum size
of an Ethernet frame.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2022-01-26 06:45:31 +01:00
parent 34872fadec
commit be265eef06
1 changed files with 3 additions and 3 deletions
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6
tcp.c
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@ -1671,7 +1671,7 @@ static int tcp_send_to_tap(struct ctx *c, struct tcp_tap_conn *conn, int flags,
} }
if (flags & SYN) { if (flags & SYN) {
uint16_t mss; int mss;
/* Options: MSS, NOP and window scale (8 bytes) */ /* Options: MSS, NOP and window scale (8 bytes) */
optlen = OPT_MSS_LEN + 1 + OPT_WS_LEN; 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 && if (c->low_wmem &&
!conn->local && !tcp_rtt_dst_low(conn)) !conn->local && !tcp_rtt_dst_low(conn))
mss = MIN(mss, PAGE_SIZE); mss = MIN(mss, PAGE_SIZE);
else else if (mss > PAGE_SIZE)
mss = ROUND_DOWN(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; data += OPT_MSS_LEN - 2;
th->doff += OPT_MSS_LEN / 4; th->doff += OPT_MSS_LEN / 4;