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pollwrap: stop returning unasked-for rwx statuses.

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The sets of poll(2) events that we check in order to return SELECT_R
and SELECT_W overlap: to be precise, they have POLLERR in common. So
if an fd signals POLLERR, then pollwrap_get_fd_rwx will respond by
saying that it has both SELECT_R and SELECT_W available on it - even
if the caller had only asked for one of those.

In other words, you can get a spurious SELECT_W notification on an fd
that you never asked for SELECT_W on in the first place. This
definitely isn't what I'd meant that API to do.

In particular, if a socket in the middle of an asynchronous connect()
signals POLLERR, then Unix Plink will call select_result for it with
SELECT_R and then SELECT_W respectively. The former will notice that
it's got an error condition and call plug_closing - and _then_ the
latter will decide that it's writable and set s->connected! The plan
was to only select it for write until it was connected, but this bug
in pollwrap was defeating that plan.

Now pollwrap_get_fd_rwx should only ever return a set of rwx flags
that's a subset of the one that the client asked for via
pollwrap_add_fd_rwx.

(cherry picked from commit 78974fce89)
This commit is contained in:
Simon Tatham 2020-02-06 23:48:36 +00:00
parent 67ca9703be
commit eccd4bf781
1 changed files with 23 additions and 8 deletions
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31
unix/uxpoll.c
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@ -126,29 +126,44 @@ int pollwrap_poll_timeout(pollwrapper *pw, int milliseconds)
return poll(pw->fds, pw->nfd, milliseconds);
}
int pollwrap_get_fd_events(pollwrapper *pw, int fd)
static void pollwrap_get_fd_events_revents(pollwrapper *pw, int fd,
int *events_p, int *revents_p)
{
pollwrap_fdtopos *f2p, f2p_find;
int events = 0, revents = 0;
assert(fd >= 0);
f2p_find.fd = fd;
f2p = find234(pw->fdtopos, &f2p_find, NULL);
if (!f2p)
return 0;
if (f2p) {
events = pw->fds[f2p->pos].events;
revents = pw->fds[f2p->pos].revents;
}
return pw->fds[f2p->pos].revents;
if (events_p)
*events_p = events;
if (revents_p)
*revents_p = revents;
}
int pollwrap_get_fd_events(pollwrapper *pw, int fd)
{
int revents;
pollwrap_get_fd_events_revents(pw, fd, NULL, &revents);
return revents;
}
int pollwrap_get_fd_rwx(pollwrapper *pw, int fd)
{
int revents = pollwrap_get_fd_events(pw, fd);
int events, revents;
pollwrap_get_fd_events_revents(pw, fd, &events, &revents);
int rwx = 0;
if (revents & SELECT_R_OUT)
if ((events & POLLIN) && (revents & SELECT_R_OUT))
rwx |= SELECT_R;
if (revents & SELECT_W_OUT)
if ((events & POLLOUT) && (revents & SELECT_W_OUT))
rwx |= SELECT_W;
if (revents & SELECT_X_OUT)
if ((events & POLLPRI) && (revents & SELECT_X_OUT))
rwx |= SELECT_X;
return rwx;
}