Rework CA certificate support to allow rootless containers

This patch includes several improvements and simplifications in CA certificate handling:

* Support for CA certificates in containers running as a non-root user
* Support for CA certificates in containers running with read-only filesystem
* Unification of Docker entrypoint scripts into one
* Entrypoint script now exports CACERT environment variable to point to the used truststore file

Docs updates at https://github.com/docker-library/official-images/ pending.

Possibly fixes: #464

Author: rassie

.test/tests/java-ca-certificates-update/certs/README.md

@@ -1 +1 @@
-This certificate/key pair has been generated with `openssl req -nodes -new -x509 -days 358000 -subj "/DC=Temurin/CN=DockerBuilder" -keyout certs/server.key -out certs/server.crt` and is only used for testing
+This certificate/key pair has been generated with `openssl req -nodes -new -x509 -days 358000 -subj "/DC=Temurin/CN=DockerBuilder" -keyout certs/dockerbuilder.key -out certs/dockerbuilder.crt` and is only used for testing

.test/tests/java-ca-certificates-update/certs/server.crt renamed to .test/tests/java-ca-certificates-update/certs/dockerbuilder.crt

@@ -1 +1 @@
-0101010001
+01010100010101010001

.test/tests/java-ca-certificates-update/certs/server.key renamed to .test/tests/java-ca-certificates-update/certs/dockerbuilder.key

@@ -1,40 +1,38 @@
 #!/bin/bash
 
-set -o pipefail 
+set -o pipefail
 
 testDir="$(readlink -f "$(dirname "$BASH_SOURCE")")"
 runDir="$(dirname "$(readlink -f "$BASH_SOURCE")")"
 
-# Find Java major/minor/build/patch version
-# 
-# https://stackoverflow.com/a/74459237/6460
-IFS='"' read -r _ java_version_string _ < <(docker run "$1" java -version 2>&1)
-IFS='._' read -r \
-    java_version_major \
-    java_version_minor \
-    java_version_build \
-    java_version_patch \
-    <<<"$java_version_string"
-
 # CMD1 in each run is just a `date` to make sure nothing is broken with or without the entrypoint
 CMD1=date
 
-# CMD2 in each run is to check for the `dockerbuilder` certificate in the Java keystore
-if [ "$java_version_major" -lt 11 ]; then
-    # We are working with JDK/JRE 8
-    #
-    # `keytool` from JDK/JRE 8 does not have the `-cacerts` option and also does not have standardized location for the
-    # `cacerts` file between the JDK and JRE, so we'd want to check both possible locations.
-    CACERTS=/opt/java/openjdk/lib/security/cacerts
-    CACERTS2=/opt/java/openjdk/jre/lib/security/cacerts
-
-    CMD2=(sh -c "keytool -list -keystore $CACERTS -storepass changeit -alias dockerbuilder || keytool -list -keystore $CACERTS2 -storepass changeit -alias dockerbuilder")
-else
-    CMD2=(keytool -list -cacerts -storepass changeit -alias dockerbuilder)
-fi
-
-# 
-# We need to use `docker run`, since `run-in-container.sh` overwrites the entrypoint
+# CMD2 in each run is to check for the `dockerbuilder` certificate in the Java keystore. Entrypoint export $CACERT to
+# point to the Java keystore.
+CMD2=(sh -c "keytool -list -keystore \$CACERT -storepass changeit -alias dockerbuilder")
+
+# For a custom entrypoint test, we need to create a new image. This image will get cleaned up at the end of the script
+# by the `finish` trap function.
+TESTIMAGE=$1.test
+
+function finish {
+    docker rmi "$TESTIMAGE" >&/dev/null
+}
+trap finish EXIT HUP INT TERM
+
+# But first, we need to create an image with an overridden entrypoint
+docker build -t "$1.test" "$runDir" -f - <<EOF >&/dev/null
+FROM $1
+COPY custom-entrypoint.sh /
+ENTRYPOINT ["/custom-entrypoint.sh"]
+EOF
+
+# NB: In this script, we need to use `docker run` explicitely, since the normally used `run-in-container.sh` overwrites
+# the entrypoint.
+
+#
+# PHASE 1: Root containers
 #
 
 # Test run 1: No added certificates and environment variable is not set. We expect CMD1 to succeed and CMD2 to fail.
@@ -63,24 +61,47 @@ echo -n $?
 docker run --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$1" "${CMD2[@]}" >&/dev/null
 echo -n $?
 
-TESTIMAGE=$1.test
+# Test run 5: Certificates are mounted and the environment variable is set, but the entrypoint is overridden. We expect
+# CMD1 to succeed and CMD2 to fail.
+docker run --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" $CMD1 >&/dev/null
+echo -n $?
+docker run --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" "${CMD2[@]}" >&/dev/null
+echo -n $?
 
-function finish {
-    docker rmi "$TESTIMAGE" >&/dev/null
-}
-trap finish EXIT HUP INT TERM
+#
+# PHASE 2: Non-root containers
+#
+
+# Test run 1: No added certificates and environment variable is not set. We expect CMD1 to succeed and CMD2 to fail.
+docker run --read-only --user 1000:1000 --rm "$1" $CMD1 >&/dev/null
+echo -n $?
+docker run --read-only --user 1000:1000 --rm "$1" "${CMD2[@]}" >&/dev/null
+echo -n $?
+
+# Test run 2: No added certificates, but the environment variable is set. Since there are no certificates, we still
+# expect CMD1 to succeed and CMD2 to fail.
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 "$1" $CMD1 >&/dev/null
+echo -n $?
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 "$1" "${CMD2[@]}" >&/dev/null
+echo -n $?
+
+# Test run 3: Certificates are mounted, but the environment variable is not set, i.e. certificate importing should not
+# be activated. We expect CMD1 to succeed and CMD2 to fail.
+docker run --read-only --user 1000:1000 --rm --volume=$testDir/certs:/certificates "$1" $CMD1 >&/dev/null
+echo -n $?
+docker run --read-only --user 1000:1000 --rm --volume=$testDir/certs:/certificates "$1" "${CMD2[@]}" >&/dev/null
+echo -n $?
+
+# Test run 4: Certificates are mounted and the environment variable is set. We expect both CMD1 and CMD2 to succeed.
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$1" $CMD1 >&/dev/null
+echo -n $?
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$1" "${CMD2[@]}" >&/dev/null
+echo -n $?
 
 # Test run 5: Certificates are mounted and the environment variable is set, but the entrypoint is overridden. We expect
 # CMD1 to succeed and CMD2 to fail.
 #
-# But first, we need to create an image with an overridden entrypoint
-docker build -t "$1.test" "$runDir" -f - <<EOF >&/dev/null 
-FROM $1
-COPY custom-entrypoint.sh /
-ENTRYPOINT ["/custom-entrypoint.sh"]
-EOF
-
-docker run --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" $CMD1 >&/dev/null
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" $CMD1 >&/dev/null
 echo -n $?
-docker run --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" "${CMD2[@]}" >&/dev/null
+docker run --read-only --user 1000:1000 -v /tmp --rm -e USE_SYSTEM_CA_CERTS=1 --volume=$testDir/certs:/certificates "$TESTIMAGE" "${CMD2[@]}" >&/dev/null
 echo -n $?

.test/tests/java-ca-certificates-update/expected-std-out.txt

@@ -0,0 +1,89 @@
+#!/usr/bin/env sh
+# Converted to POSIX shell to avoid the need for bash in the image
+
+set -e
+
+# JDK truststore location
+CACERT=$JAVA_HOME/lib/security/cacerts
+
+# JDK8 puts its JRE in a subdirectory
+if [ -f "$JAVA_HOME/jre/lib/security/cacerts" ]; then
+    CACERT=$JAVA_HOME/jre/lib/security/cacerts
+fi
+
+# Opt-in is only activated if the environment variable is set
+if [ -n "$USE_SYSTEM_CA_CERTS" ]; then
+
+    if [ ! -w /tmp ]; then
+        echo "Using additional CA certificates requires write permissions to /tmp. Cannot create truststore."
+        exit 1
+    fi
+
+    # Figure out whether we can write to the JVM truststore. If we can, we'll add the certificates there. If not,
+    # we'll use a temporary truststore.
+    if [ ! -w "$CACERT" ]; then
+        # We cannot write to the JVM truststore, so we create a temporary one
+        CACERT_NEW=$(mktemp)
+        echo "Using a temporary truststore at $CACERT_NEW"
+        cp $CACERT $CACERT_NEW
+        CACERT=$CACERT_NEW
+        # If we use a custom truststore, we need to make sure that the JVM uses it
+        export JAVA_TOOL_OPTIONS="${JAVA_TOOL_OPTIONS} -Djavax.net.ssl.trustStore=${CACERT} -Djavax.net.ssl.trustStorePassword=changeit"
+    fi
+
+    tmp_store=$(mktemp)
+
+    # Copy full system CA store to a temporary location
+    trust extract --overwrite --format=java-cacerts --filter=ca-anchors --purpose=server-auth "$tmp_store"
+
+    # Add the system CA certificates to the JVM truststore.
+    keytool -importkeystore -destkeystore "$CACERT" -srckeystore "$tmp_store" -srcstorepass changeit -deststorepass changeit -noprompt # >/dev/null
+
+    # Import the additional certificate into JVM truststore
+    for i in /certificates/*crt; do
+        if [ ! -f "$i" ]; then
+            continue
+        fi
+        keytool -import -noprompt -alias "$(basename "$i" .crt)" -file "$i" -keystore "$CACERT" -storepass changeit # >/dev/null
+    done
+
+    # Add additionation certificates to the system CA store. This requires write permissions to several system
+    # locations, which is not possible in a container with read-only filesystem and/or non-root container.
+    if [ "$(id -u)" -eq 0 ]; then
+
+        # Copy certificates from /certificates to the system truststore, but only if the directory exists and is not empty.
+        # The reason why this is not part of the opt-in is because it leaves open the option to mount certificates at the
+        # system location, for whatever reason.
+        if [ -d /certificates ] && [ "$(ls -A /certificates 2>/dev/null)" ]; then
+
+            # UBI/CentOS
+            if [ -d /usr/share/pki/ca-trust-source/anchors/ ]; then
+                cp -a /certificates/* /usr/share/pki/ca-trust-source/anchors/
+            fi
+
+            # Ubuntu/Alpine
+            if [ -d /usr/local/share/ca-certificates/ ]; then
+                cp -a /certificates/* /usr/local/share/ca-certificates/
+            fi
+        fi
+
+        # UBI/CentOS
+        if which update-ca-trust >/dev/null; then
+            update-ca-trust
+        fi
+
+        # Ubuntu/Alpine
+        if which update-ca-certificates >/dev/null; then
+            update-ca-certificates
+        fi
+    else
+        # If we are not root, we cannot update the system truststore. That's bad news for tools like `curl` and `wget`,
+        # but since the JVM is the primary focus here, we can live with that.
+        true
+    fi
+fi
+
+# Let's provide a variable with the correct path for tools that want or need to use it
+export CACERT
+
+exec "$@"