ipc: recv_cmd4 clobbers destination buffer on errors

Handling this should be done at the lowest levels possible;
so away from higher-level lei code.

5 files changed, 13 insertions, 7 deletions

diff --git a/lib/PublicInbox/CmdIPC4.pm b/lib/PublicInbox/CmdIPC4.pm
index 99890244..4bc4c729 100644
--- a/lib/PublicInbox/CmdIPC4.pm
+++ b/lib/PublicInbox/CmdIPC4.pm
@@ -31,7 +31,10 @@ no warnings 'once';
 *recv_cmd4 = sub ($$$) {
         my ($s, undef, $len) = @_; # $_[1] = destination buffer
         my $mh = Socket::MsgHdr->new(buflen => $len, controllen => 256);
-        my $r = Socket::MsgHdr::recvmsg($s, $mh, 0) // return (undef);
+        my $r = Socket::MsgHdr::recvmsg($s, $mh, 0) // do {
+                $_[1] = '';
+                return (undef);
+        };
         $_[1] = $mh->buf;
         return () if $r == 0;
         my (undef, undef, $data) = $mh->cmsghdr;
diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index 8b62def2..1ead9bf6 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -1167,7 +1167,6 @@ sub event_step {
                 if (scalar(@fds) == 1 && !defined($fds[0])) {
                         return if $! == EAGAIN;
                         die "recvmsg: $!" if $! != ECONNRESET;
-                        $buf = '';
                         @fds = (); # for open loop below:
                 }
                 for (@fds) { open my $rfh, '+<&=', $_ }
diff --git a/lib/PublicInbox/LeiSelfSocket.pm b/lib/PublicInbox/LeiSelfSocket.pm
index 84367266..b8745252 100644
--- a/lib/PublicInbox/LeiSelfSocket.pm
+++ b/lib/PublicInbox/LeiSelfSocket.pm
@@ -25,7 +25,6 @@ sub event_step {
         if (scalar(@fds) == 1 && !defined($fds[0])) {
                 return if $!{EAGAIN};
                 die "recvmsg: $!" unless $!{ECONNRESET};
-                $buf = '';
         } else { # just in case open so perl can auto-close them:
                 for (@fds) { open my $fh, '+<&=', $_ };
         }
diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index ed698afc..2b84e2d5 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -259,10 +259,12 @@ void recv_cmd4(PerlIO *s, SV *buf, STRLEN n)
         msg.msg_controllen = CMSG_SPACE(SEND_FD_SPACE);
 
         i = recvmsg(PerlIO_fileno(s), &msg, 0);
-        if (i < 0)
-                Inline_Stack_Push(&PL_sv_undef);
-        else
+        if (i >= 0) {
                 SvCUR_set(buf, i);
+        } else {
+                Inline_Stack_Push(&PL_sv_undef);
+                SvCUR_set(buf, 0);
+        }
         if (i > 0 && cmsg.hdr.cmsg_level == SOL_SOCKET &&
                         cmsg.hdr.cmsg_type == SCM_RIGHTS) {
                 size_t len = cmsg.hdr.cmsg_len;
diff --git a/lib/PublicInbox/Syscall.pm b/lib/PublicInbox/Syscall.pm
index 0a0912fb..776fbe23 100644
--- a/lib/PublicInbox/Syscall.pm
+++ b/lib/PublicInbox/Syscall.pm
@@ -444,7 +444,10 @@ no warnings 'once';
                         msg_controllen,
                         0); # msg_flags
         my $r = syscall($SYS_recvmsg, fileno($sock), $mh, 0);
-        return (undef) if $r < 0; # $! set
+        if ($r < 0) { # $! is set
+                $_[1] = '';
+                return (undef);
+        }
         substr($_[1], $r, length($_[1]), '');
         my @ret;
         if ($r > 0) {