Bug #34380: preserve errno for stream_select and stream_socket_pair

[zackse]

When the system calls underneath stream_select() and stream_socket_pair()
fail, errno is logged but is not preserved. This change preservers errno in
posix_globals to allow the caller to query posix_get_last_error() to determine
the cause of the failure.

Previously there wasn't any way to differentiate between a signal interrupt
(EINTR) and other errors, making proper error handling/recovery difficult or
impossible.

[zackse]

Example stream_socket_pair -- should print 95 (Operation not supported), always prints 0.

# php -r 'stream_socket_pair(STREAM_PF_INET, STREAM_SOCK_STREAM, STREAM_IPPROTO_IP); echo posix_get_last_error(), "\n";'

Example stream_select -- should print 4 (Interrupted system call), always prints 0.
In one terminal:

# php -a
function handler($signo) {
    echo "got signal $signo\n";
}
# SIGUSR2
pcntl_signal(12, "handler");

$open_spec = array(0 => array('pipe','r'), 1 => array('pipe', 'w'), 2 => array('pipe','w'));
$proc = proc_open('/bin/sleep 60', $open_spec, $pipes, NULL, $_ENV);

$reads = array($pipes[1], $pipes[2]);
$writes = null;
$except = null;
$ready = stream_select($reads, $writes, $except, 60);
echo posix_get_last_error(), "\n";

In another terminal:

# pkill -f 'php -a'

Observe output in first terminal.

[auroraeosrose]

The problem with this is it adds a dependency on the posix extension - which breaks things on systems without it or when PHP is not compiled with the posix extension or if the extension isn't loaded

I would suggest instead adding a C api function in the posix extension to set that information, check for the posix extension being loaded and then hit that C api to set the information in the posix extension globals

[zackse]

Thanks for the feedback. I reworked the implementation as you suggested. Note that I didn't expose the "set" call to PHP because it doesn't seem to be generally useful, but my perspective may be way off because I don't use PHP regularly.

[krakjoe]

Since this targets a security fix only branch, and since it has merge conflicts, and since it would need to look different against a supported branch, I'm closing this PR.

Please take this action as encouragement to open a clean PR against a supported branch.

On a side note, the patch still doesn't look right to me, not only is it strange for streams to have some kind of soft dependency on posix, but the new function is called unconditionally while header is included conditionally. This may be the reason that nobody merged it when PHP 5 was still in active development.