syscall: fix valgrind error in pure Perl send_cmd4

We need to allocate CMSG_SPACE for the `struct cmsghdr', not the
smaller CMSG_LEN.  AFAIK this isn't a real world problem since
the Linux kernel doesn't care about the uninitialized space as
long as memory region belongs to the user, but valgrind complains.

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/PublicInbox/Syscall.pm b/lib/PublicInbox/Syscall.pm
index b76a9e8a..4cf45d0f 100644
--- a/lib/PublicInbox/Syscall.pm
+++ b/lib/PublicInbox/Syscall.pm
@@ -398,10 +398,13 @@ no warnings 'once';
         my ($sock, $fds, undef, $flags) = @_;
         my $iov = pack('P'.TMPL_size_t,
                         $_[2] // NUL, length($_[2] // NUL) || 1);
+        my $fd_space = scalar(@$fds) * SIZEOF_int;
+        my $msg_controllen = CMSG_SPACE($fd_space);
         my $cmsghdr = pack(TMPL_size_t . # cmsg_len
                         'LL' .  # cmsg_level, cmsg_type,
-                        ('i' x scalar(@$fds)),
-                        CMSG_LEN(scalar(@$fds) * SIZEOF_int), # cmsg_len
+                        ('i' x scalar(@$fds)) . # CMSG_DATA
+                        '@'.($msg_controllen - 1).'x1', # pad to space, not len
+                        CMSG_LEN($fd_space), # cmsg_len
                         SOL_SOCKET, SCM_RIGHTS, # cmsg_{level,type}
                         @$fds); # CMSG_DATA
         my $mh = pack('PL' . # msg_name, msg_namelen (socklen_t (U32))
@@ -413,7 +416,7 @@ no warnings 'once';
                         @BYTES_4_hole,
                         $iov, 1, # msg_iov, msg_iovlen
                         $cmsghdr, # msg_control
-                        CMSG_SPACE(scalar(@$fds) * SIZEOF_int), # msg_controllen
+                        $msg_controllen,
                         0); # msg_flags
         my $sent;
         my $try = 0;