Only return file descriptors to block or character devices

If the requested path contained a slash, opendev(3) blindly opened the file
and returned a file descriptor to it.

Check for block or character devices (according to OPENDEV_BLCK) and fail
for other types.

Spotted through installboot(8) which happily opened a stage file as device
when forgetting the device argument:
	# installboot -v ./biosboot
	Using / as root
	installing bootstrap on ./biosboot
	using first-stage /usr/mdec/biosboot, second-stage /usr/mdec/boot
	installboot: disklabel: ./biosboot: Inappropriate ioctl for device

This makes it fail earlier, as expected:
	# installboot -v ./biosboot
	installboot: open: ./biosboot: Block device required

The case where opendev(3) is passed a string not containing a slash, i.e.
a supposed DUID, is fine, as diskmap(4) will ensure that only valid device
paths are returned, if the DUID is valid.

Feedback OK millert

1 files changed, 7 insertions, 5 deletions

diff --git a/lib/libutil/opendev.3 b/lib/libutil/opendev.3
index 65535a6fdde..ae6ce343007 100644
--- a/lib/libutil/opendev.3
+++ b/lib/libutil/opendev.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: opendev.3,v 1.22 2015/01/15 19:06:32 schwarze Exp $
+.\"	$OpenBSD: opendev.3,v 1.23 2022/08/25 17:09:54 kn Exp $
 .\"
 .\" Copyright (c) 2000, Todd C. Miller.  All rights reserved.
 .\" Copyright (c) 1996, Jason Downs.  All rights reserved.
@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: January 15 2015 $
+.Dd $Mdocdate: August 25 2022 $
 .Dt OPENDEV 3
 .Os
 .Sh NAME
@@ -90,10 +90,12 @@ is not
 .Dv NULL ,
 it is modified to point at the fully expanded device name.
 .Sh RETURN VALUES
-The
+If successful,
 .Fn opendev
-return value and errors are the same as the return value and errors of
-.Xr open 2 .
+returns a file descriptor.
+Otherwise, a value of -1 is returned and
+.Va errno
+is set to indicate the error.
 .Sh SEE ALSO
 .Xr open 2 ,
 .Xr getrawpartition 3 ,