challenge: compile kp program inside alpine to avoid linking to glibc

Makefile

@@ -1,4 +1,4 @@
-all: login-app/login-app token-validator/token-validator pkg/challenge/kp
+all: login-app/login-app token-validator/token-validator
 
 fonts: fonts/Inconsolata-16b.psf fonts/Inconsolata-16r.psf fonts/Inconsolata-32b.psf fonts/Inconsolata-32r.psf
 fonts/Inconsolata-16b.psf:
@@ -10,9 +10,6 @@ fonts/Inconsolata-32b.psf:
 fonts/Inconsolata-32r.psf:
 	wget https://github.com/xeechou/Inconsolata-psf/raw/master/Inconsolata-32r.psf
 
-pkg/challenge/kp: pkg/challenge/kp.c
-	gcc -o $@ $+
-
 token-validator/token-validator: token-validator/*.go
 	go generate ./token-validator
 	GOOS=linux GOARM=5 GOARCH=arm go build -tags netgo -ldflags '-w -extldflags "-static"' -o $@ ./token-validator

challenge.yml

@@ -1,5 +1,5 @@
 init:
-  - nemunaire/challenge:e0d9663aba0794fb455be9844eed30793d4fb9fb-dirty
+  - nemunaire/challenge:6eb16abb6c584ad6a82b9518968014d145decd38
 
 files:
   - path: etc/motd
@@ -34,9 +34,6 @@ files:
   - path: bin/adlin
     source: pkg/challenge/adlin
     mode: "0755"
-  - path: usr/bin/init-crypto
-    source: pkg/challenge/kp
-    mode: "0755"
   - path: etc/issue
     source: pkg/challenge/issue
     mode: "0644"

pkg/challenge/Dockerfile

@@ -5,7 +5,10 @@ RUN mkdir -p /out/etc/apk/ && \
     cp -r /etc/apk/keys /out/etc/apk/keys
 
 RUN apk add --no-cache \
-    mdocml-apropos
+    gcc \
+    linux-headers \
+    mdocml-apropos \
+    musl-dev
 
 RUN apk add --no-cache --initdb -p /out \
     alpine-baselayout \
@@ -53,6 +56,9 @@ RUN makewhatis /out/usr/share/man
 
 RUN rm -rf /out/etc/inittab
 
+COPY kp.c /root/kp.c
+RUN gcc -o /out/usr/bin/init-crypto /root/kp.c
+
 
 FROM scratch