From: Klemens Nanni <kn@openbsd.org>
Subject: Re: installer, rc: unify random seeding
To: OpenBSD tech <tech@openbsd.org>, Theo de Raadt <deraadt@openbsd.org>
Date: Sun, 18 May 2025 08:43:15 +0000

03.05.2025 02:29, Klemens Nanni пишет:
> No behaviour change, just, imho, simpler and cleaner code.
> 
> The installer has feed_random() plus store_random() and rc(8) has random_seed().
> 
> Call both store_random() and use the same wording to match, use variables for
> brevity and to tell what the files are used for.
> 
> Replace the absoloute octal mode to chmod(8) with symbolic (relative) one to
> explicitly show that this is where userland strips the sticky bit set by the
> bootloader to help itself:  if set, seeds are skipped with
> 
> 	NOTE: random seed is being reused.
> 
> (If your root is a softraid, you never see this as bootloaders cannot write to it
>  and thus never sets +t in the first place.)
> 
> Always call the function on shutdown and silence just stderr (stdout already
> is quiet) instead of doing a preemptive append for brevity:  the reason for
> the current brief message is rc r1.437 from 2014:
> 
>     Print a warning message if the files with the random seed are not
>     writeable during shutdown.  This prevents ugly error messages when
>     the machine is rebooted from singe-user without mounting the file
>     systems read-write.
> 
> Feedback? OK?

Ping.

Same diff with better comment from Theo.

Index: distrib/miniroot/install.sub
===================================================================
RCS file: /cvs/src/distrib/miniroot/install.sub,v
diff -u -p -r1.1270 install.sub
--- distrib/miniroot/install.sub	4 May 2025 12:32:41 -0000	1.1270
+++ distrib/miniroot/install.sub	8 May 2025 09:58:48 -0000
@@ -2932,12 +2932,17 @@ encr_pwd() {
 	fi
 }
 
-# Store entropy for the next boot.
+# Create future seeds for the bootloader and rc(8).
 store_random() {
-	dd if=/dev/random of=/mnt/var/db/host.random bs=65536 count=1 \
-		status=none
-	dd if=/dev/random of=/mnt/etc/random.seed bs=512 count=1 status=none
-	chmod 600 /mnt/var/db/host.random /mnt/etc/random.seed
+	local _bootseed=/mnt/etc/random.seed _hostseed=/mnt/var/db/host.random
+
+	dd if=/dev/random of=$_bootseed bs=512   count=1 status=none
+	dd if=/dev/random of=$_hostseed bs=65536 count=1 status=none
+
+	# Removal of the sticky bit indicates the file has fresh contents for
+	# use by a subsequent bootloader (who sets the sticky bit to prevent
+	# content reuse).
+	chmod u=rw-t,go= $_bootseed $_hostseed
 }
 
 # Final steps common for installs and upgrades.
@@ -3068,7 +3073,7 @@ __EOT
 		fi
 	fi
 
-	# Store entropy for the next boot.
+	# Update seed files.
 	store_random
 
 	# Pat on the back.
Index: etc/rc
===================================================================
RCS file: /cvs/src/etc/rc,v
diff -u -p -r1.580 rc
--- etc/rc	7 Apr 2025 14:49:26 -0000	1.580
+++ etc/rc	8 May 2025 09:58:48 -0000
@@ -72,14 +72,20 @@ wsconsctl_conf() {
 	done
 }
 
-# Push the old seed into the kernel, create a future seed  and create a seed
-# file for the boot-loader.
-random_seed() {
-	dd if=/var/db/host.random of=/dev/random bs=65536 count=1 status=none
-	chmod 600 /var/db/host.random
-	dd if=/dev/random of=/var/db/host.random bs=65536 count=1 status=none
-	dd if=/dev/random of=/etc/random.seed bs=512 count=1 status=none
-	chmod 600 /etc/random.seed
+# Push the old seed into the kernel and create future seeds for the bootloader,
+# the installer and rc(8).
+store_random() {
+	local _bootseed=/etc/random.seed _hostseed=/var/db/host.random
+
+	dd if=$_hostseed of=/dev/random bs=65536 count=1 status=none
+
+	dd if=/dev/random of=$_bootseed bs=512   count=1 status=none
+	dd if=/dev/random of=$_hostseed bs=65536 count=1 status=none
+
+	# Removal of the sticky bit indicates the file has fresh contents for
+	# use by a subsequent bootloader (who sets the sticky bit to prevent
+	# content reuse).
+	chmod u=rw-t,go= $_bootseed $_hostseed
 }
 
 # Populate net.inet.(tcp|udp).baddynamic with the contents of /etc/services so
@@ -351,12 +357,8 @@ _rc_parse_conf
 # - execute the rc.d scripts specified by $pkg_scripts in reverse order
 # - bring carp interfaces down gracefully
 if [[ $1 == shutdown ]]; then
-	if echo 2>/dev/null >>/var/db/host.random ||
-	    echo 2>/dev/null >>/etc/random.seed; then
-		random_seed
-	else
-		echo warning: cannot write random seed to disk
-	fi
+	store_random 2>/dev/null ||
+		echo 'warning: cannot write random seed to disk'
 
 	# If we are in secure level 0, assume single user mode.
 	if (($(sysctl -n kern.securelevel) == 0)); then
@@ -490,7 +492,7 @@ sh /etc/netstart
 
 start_daemon unwind >/dev/null 2>&1
 
-random_seed
+store_random
 
 wait_reorder_libs