Bug 1699793

+++ This bug was initially created as a clone of Bug #1693293 +++

It seems inet_aton should be thread safe (see https://stackoverflow.com/questions/2319469/is-perls-inet-aton-thread-safe) so there might be a bug with RHEL7's Perl.

[...]

and indeed, adding breakpoints to gethostbyname and gethostbyname_r it shows
gethostbyname is called from a thread; should call only gethostbyname_r.

Breakpoint 1, 0x00007ffff68096a0 in gethostbyname () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff68096a0 in gethostbyname () from /lib64/libc.so.6
#1  0x00007fffef7a2363 in XS_Socket_inet_aton () from /usr/lib64/perl5/vendor_perl/auto/Socket/Socket.so
#2  0x00007ffff7b093ef in Perl_pp_entersub () from /usr/lib64/perl5/CORE/libperl.so
#3  0x00007ffff7b01b66 in Perl_runops_standard () from /usr/lib64/perl5/CORE/libperl.so
#4  0x00007ffff7a99148 in Perl_call_sv () from /usr/lib64/perl5/CORE/libperl.so
#5  0x00007fffefdbdcf9 in S_ithread_run () from /usr/lib64/perl5/vendor_perl/auto/threads/threads.so
#6  0x00007ffff6ac5dd5 in start_thread () from /lib64/libpthread.so.0
#7  0x00007ffff67eeead in clone () from /lib64/libc.so.6

[...]

--- Additional comment from Petr Pisar on 2019-03-27 16:22:18 GMT ---

Thank you for the report. I confirm I can reproduce the issue.

The inet_aton() function is provided by Socket Perl module and it indeed calls gethostbyname() that is not thread-safe:

void
inet_aton(host)
    char *  host
    CODE:
    {
    struct in_addr ip_address;
    struct hostent * phe;

    if ((*host != '\0') && inet_aton(host, &ip_address)) {
        ST(0) = sv_2mortal(newSVpvn((char *)&ip_address, sizeof(ip_address)));
        XSRETURN(1);
    }

→   phe = gethostbyname(host);
    if (phe && phe->h_addrtype == AF_INET && phe->h_length == 4) {
        ST(0) = sv_2mortal(newSVpvn((char *)phe->h_addr, phe->h_length));
        XSRETURN(1);
    }

    XSRETURN_UNDEF;
    }

As a workaround I recommend using getaddrinfo() from the same Socket module instead. It's thread safe and supports IPv6. As replacement for IO:Socket::INET I recommend IO::Socket::IP instead.

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RHEL-8 is affected (perl-Socket-2.027-2.el8, perl-Socket-2.027-3.module+el8.1.0+2926+ce7246ad).