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tcp: Clamp MSS depending on IP version, properly derive buffer sizes

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It makes no sense to include an IPv6 header in the calculation for
clamping MSS on IPv4.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2021-10-15 17:09:37 +02:00
parent bf63832207
commit 54e6513d17
1 changed files with 19 additions and 17 deletions
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36
tcp.c
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@ -352,6 +352,11 @@
#define MAX_WS 10
#define MAX_WINDOW (1 << (16 + (MAX_WS)))
#define MSS_DEFAULT 536
#define MSS4 (USHRT_MAX - sizeof(uint32_t) - sizeof(struct ethhdr) - \
sizeof(struct iphdr) - sizeof(struct tcphdr))
#define MSS6 (USHRT_MAX - sizeof(uint32_t) - sizeof(struct ethhdr) - \
sizeof(struct ipv6hdr) - sizeof(struct tcphdr))
#define WINDOW_DEFAULT 14600 /* RFC 6928 */
#define SYN_TIMEOUT 240000 /* ms */
@ -590,7 +595,8 @@ static struct tcp4_l2_buf_t {
struct ethhdr eh; /* 30 14 */
struct iphdr iph; /* 44 28 */
struct tcphdr th; /* 64 48 */
uint8_t data[USHRT_MAX - sizeof(struct tcphdr)];
uint8_t data[MSS4]; /* 84 68 */
/* 65541 65525 */
#ifdef __AVX2__
} __attribute__ ((packed, aligned(32)))
#else
@ -622,8 +628,8 @@ struct tcp6_l2_buf_t {
struct ethhdr eh; /* 18 6 */
struct ipv6hdr ip6h; /* 32 20 */
struct tcphdr th; /* 72 60 */
uint8_t data[USHRT_MAX -
(sizeof(struct ipv6hdr) + sizeof(struct tcphdr))];
uint8_t data[MSS6]; /* 92 80 */
/* 65639 65627 */
#ifdef __AVX2__
} __attribute__ ((packed, aligned(32)))
#else
@ -1868,14 +1874,12 @@ static void tcp_conn_from_tap(struct ctx *c, int af, void *addr,
if (conn->mss_guest < 0)
conn->mss_guest = MSS_DEFAULT;
/* Don't upset qemu */
if (c->mode == MODE_PASST) {
/* Don't upset qemu */
conn->mss_guest = MIN(USHRT_MAX -
sizeof(uint32_t) -
sizeof(struct ethhdr) -
sizeof(struct ipv6hdr) -
sizeof(struct tcphdr),
conn->mss_guest);
if (af == AF_INET)
conn->mss_guest = MIN(MSS4, conn->mss_guest);
else
conn->mss_guest = MIN(MSS6, conn->mss_guest);
}
sl = sizeof(conn->mss_guest);
@ -2563,14 +2567,12 @@ int tcp_tap_handler(struct ctx *c, int af, void *addr,
if (conn->mss_guest < 0)
conn->mss_guest = MSS_DEFAULT;
/* Don't upset qemu */
if (c->mode == MODE_PASST) {
/* Don't upset qemu */
conn->mss_guest = MIN(USHRT_MAX -
sizeof(uint32_t) -
sizeof(struct ethhdr) -
sizeof(struct ipv6hdr) -
sizeof(struct tcphdr),
conn->mss_guest);
if (af == AF_INET)
conn->mss_guest = MIN(MSS4, conn->mss_guest);
else
conn->mss_guest = MIN(MSS6, conn->mss_guest);
}
/* info.tcpi_bytes_acked already includes one byte for SYN, but