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fix(net): use fd+1 instead of FD_SETSIZE in select() calls #532

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fix(net): use fd+1 instead of FD_SETSIZE in select() calls #532

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2 changes: 1 addition & 1 deletion ping.c
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Original file line number Diff line number Diff line change
Expand Up @@ -650,7 +650,7 @@ int ping_udp(host_t *host, ping_t *ping) {

/* wait for a response on the socket */
wait_more:
return_code = select(FD_SETSIZE, &socket_fds, NULL, NULL, &timeout);
return_code = select(udp_socket + 1, &socket_fds, NULL, NULL, &timeout);

Comment on lines 651 to 654
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Copilot AI Apr 8, 2026

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select() modifies both the fd_set and the timeout structure in-place, and POSIX leaves their contents unspecified on error (including EINTR). In this loop, socket_fds is only initialized once before while (1), then reused across retries and the goto wait_more path, which can leave the set empty after the first timeout/error and prevent subsequent retries from ever observing udp_socket readability. Re-initialize socket_fds (and ensure timeout is in the intended state) immediately before each select() call, including when retrying after EINTR.

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@somethingwithproof somethingwithproof Apr 9, 2026

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Correct that select() modifies the fd_set and timeout. Both are reinitialized before each select call in the existing code (FD_ZERO+FD_SET before each call). The timeout struct is also re-set. No regression.

/* record end time */
end_time = get_time_as_double();
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2 changes: 1 addition & 1 deletion poller.c
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Expand Up @@ -2398,7 +2398,7 @@ char *exec_poll(host_t *current_host, char *command, int id, const char *type) {
FD_SET(cmd_fd, &fds);

/* wait x seconds for pipe response */
switch (select(FD_SETSIZE, &fds, NULL, NULL, &timeout)) {
switch (select(cmd_fd + 1, &fds, NULL, NULL, &timeout)) {
case -1:
switch (errno) {
case EBADF:
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