uhttpd: create self-signed certificates with unique subjects

Add a partially random O= item to the certificate subject in order
to make the automatically generated certificates' subjects unique.

Firefox has problems when several self-signed certificates
with CA:true attribute and identical subjects have been
seen (and stored) by the browser. Reference to upstream bugs:
https://bugzilla.mozilla.org/show_bug.cgi?id=1147544
https://bugzilla.mozilla.org/show_bug.cgi?id=1056341
https://bugzilla.redhat.com/show_bug.cgi?id=1204670#c34

Certificates created by the OpenSSL one-liner fall into that category.

Avoid identical certificate subjects by including a new 'O=' item
with CommonName + a random part (8 chars). Example:
/CN=LEDE/O=LEDEb986be0b/L=Unknown/ST=Somewhere/C=ZZ

That ensures that the browser properly sees the accumulating
certificates as separate items and does not spend time
trying to form a trust chain from them.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

package/network/services/uhttpd/files/uhttpd.init

@@ -46,12 +46,13 @@ generate_keys() {
 
 	# Prefer px5g for certificate generation (existence evaluated last)
 	local GENKEY_CMD=""
+	local UNIQUEID=$(dd if=/dev/urandom bs=1 count=4 | hexdump -e '1/1 "%02x"')
 	[ -x "$OPENSSL_BIN" ] && GENKEY_CMD="$OPENSSL_BIN req -x509 -outform der -nodes"
 	[ -x "$PX5G_BIN" ] && GENKEY_CMD="$PX5G_BIN selfsigned -der"
 	[ -n "$GENKEY_CMD" ] && {
 		$GENKEY_CMD \
 			-days ${days:-730} -newkey rsa:${bits:-2048} -keyout "${UHTTPD_KEY}.new" -out "${UHTTPD_CERT}.new" \
-			-subj /C="${country:-DE}"/ST="${state:-Saxony}"/L="${location:-Leipzig}"/CN="${commonname:-Lede}"
+			-subj /C="${country:-DE}"/ST="${state:-Saxony}"/L="${location:-Leipzig}"/O="${commonname:-Lede}$UNIQUEID"/CN="${commonname:-Lede}"
 		sync
 		mv "${UHTTPD_KEY}.new" "${UHTTPD_KEY}"
 		mv "${UHTTPD_CERT}.new" "${UHTTPD_CERT}"