Only ldapd tried to handle fd exhaustion during imsg fd passing.

Remove the getdtablecount code from imsgbuf_read() and instead
move the getdtablecount code into ldapd.

Handle EMSGSIZE (the error returned when there are not enough
free file descriptor slots) inside imsgbuf_read() by retrying
the read to receive the data but without fd.
A caller expecting an fd should check the return value of
imsg_get_fd.

OK tb@

2 files changed, 8 insertions, 11 deletions

diff --git a/lib/libutil/Symbols.map b/lib/libutil/Symbols.map
index 4d459dbc60d..aa583d3f9ef 100644
--- a/lib/libutil/Symbols.map
+++ b/lib/libutil/Symbols.map
@@ -70,7 +70,6 @@
 		imsg_compose_ibuf;
 		imsg_composev;
 		imsg_create;
-		imsg_fd_overhead;
 		imsg_forward;
 		imsg_free;
 		imsg_get;
diff --git a/lib/libutil/imsg.c b/lib/libutil/imsg.c
index f9497a47ec0..a0031c47778 100644
--- a/lib/libutil/imsg.c
+++ b/lib/libutil/imsg.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: imsg.c,v 1.31 2024/11/21 12:54:52 claudio Exp $	*/
+/*	$OpenBSD: imsg.c,v 1.32 2024/11/21 12:58:09 claudio Exp $	*/
 
 /*
  * Copyright (c) 2023 Claudio Jeker <claudio@openbsd.org>
@@ -34,8 +34,6 @@ struct imsg_fd {
 	int			fd;
 };
 
-int	 imsg_fd_overhead = 0;
-
 static int	 imsg_dequeue_fd(struct imsgbuf *);
 
 void
@@ -77,16 +75,16 @@ imsgbuf_read(struct imsgbuf *imsgbuf)
 		return (-1);
 
 again:
-	if (getdtablecount() + imsg_fd_overhead +
-	    (int)((CMSG_SPACE(sizeof(int))-CMSG_SPACE(0))/sizeof(int))
-	    >= getdtablesize()) {
-		free(ifd);
-		return (1);
-	}
-
 	if ((n = recvmsg(imsgbuf->fd, &msg, 0)) == -1) {
 		if (errno == EINTR)
 			goto again;
+		if (errno == EMSGSIZE)
+			/*
+			 * Not enough fd slots: fd passing failed, retry
+			 * to receive the message without fd.
+			 * imsg_get_fd() will return -1 in that case.
+			 */
+			goto again;
 		if (errno == EAGAIN) {
 			free(ifd);
 			return (1);