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migrate, tcp: More careful marshalling of mss parameter during migration

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During migration we extract the limit on segment size using TCP_MAXSEG,
and set it on the other side with TCP_REPAIR_OPTIONS.  However, unlike most
32-bit values we transfer we transfer it in native endian, not network
endian.  This is not correct; add it to the list of endian fixups we make.

In addition, while MAXSEG will be 32-bits in practice, and is given as such
to TCP_REPAIR_OPTIONS, the TCP_MAXSEG sockopt treats it as an 'int'.  It's
not strictly safe to pass a uint32_t to a getsockopt() expecting an int,
although we'll get away with it on most (maybe all) platforms.  Correct
this as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: Minor coding style fix]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2025-03-19 16:14:21 +11:00 • committed by Stefano Brivio
parent 51f3c071a7
commit 28772ee91a
1 changed files with 6 additions and 1 deletions

7
tcp.c
View file

@ -2848,13 +2848,16 @@ static int tcp_flow_dump_mss(const struct tcp_tap_conn *conn,
struct tcp_tap_transfer_ext *t)
{
socklen_t sl = sizeof(t->mss);
int val;
if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &t->mss, &sl)) {
if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &val, &sl)) {
int rc = -errno;
flow_perror(conn, "Getting MSS");
return rc;
}
t->mss = (uint32_t)val;
return 0;
}
@ -3301,6 +3304,7 @@ int tcp_flow_migrate_source_ext(int fd, const struct tcp_tap_conn *conn)
t->sndq = htonl(t->sndq);
t->notsent = htonl(t->notsent);
t->rcvq = htonl(t->rcvq);
t->mss = htonl(t->mss);
t->snd_wl1 = htonl(t->snd_wl1);
t->snd_wnd = htonl(t->snd_wnd);
@ -3514,6 +3518,7 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
t.sndq = ntohl(t.sndq);
t.notsent = ntohl(t.notsent);
t.rcvq = ntohl(t.rcvq);
t.mss = ntohl(t.mss);
t.snd_wl1 = ntohl(t.snd_wl1);
t.snd_wnd = ntohl(t.snd_wnd);