Harden devcontainer: pin digests, guard SYS_ADMIN, fix mount filters (#20)

Address review feedback from #14–#19:

- Pin base image and uv with SHA256 digests (#15)
- Install fzf from GitHub releases instead of apt (#14)
- Add SYS_ADMIN capability guard to prevent remount attacks (#16)
- Fix mount filter to use target paths instead of source prefixes (#17)
- Fix temp file leak in extract_mounts_to_file (#17)
- Sort apt packages alphabetically (#18)
- Remove unused Tailscale feature (#19)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: dguido

.zshrc

@@ -51,6 +51,5 @@ _fzf_compgen_dir() {
   fdfind --type d --hidden --follow --exclude .git . "$1"
 }
 
-# Source fzf key bindings and completion
-source ~/.fzf/key-bindings.zsh
-source ~/.fzf/completion.zsh
+# Source fzf shell integration (built-in since fzf 0.48+)
+eval "$(fzf --zsh)"

Dockerfile

@@ -1,6 +1,8 @@
 # Claude Code Devcontainer
 # Based on Microsoft devcontainer image for better devcontainer integration
-FROM mcr.microsoft.com/devcontainers/base:ubuntu-24.04
+ARG UV_VERSION=0.10.0
+FROM ghcr.io/astral-sh/uv:${UV_VERSION}@sha256:78a7ff97cd27b7124a5f3c2aefe146170793c56a1e03321dd31a289f6d82a04f AS uv
+FROM mcr.microsoft.com/devcontainers/base:ubuntu-24.04@sha256:d94c97dd9cacf183d0a6fd12a8e87b526e9e928307674ae9c94139139c0c6eae
 
 ARG TZ
 ENV TZ="$TZ"
@@ -13,23 +15,22 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   bubblewrap \
   socat \
   # Modern CLI tools
-  fzf \
-  ripgrep \
   fd-find \
+  ripgrep \
   tmux \
   zsh \
   # Build tools
   build-essential \
   # Utilities
   jq \
   nano \
-  vim \
   unzip \
+  vim \
   # Network tools (for security testing)
-  iptables \
+  dnsutils \
   ipset \
+  iptables \
   iproute2 \
-  dnsutils \
   && apt-get clean && rm -rf /var/lib/apt/lists/*
 
 # Install git-delta
@@ -40,7 +41,17 @@ RUN ARCH=$(dpkg --print-architecture) && \
   rm /tmp/git-delta.deb
 
 # Install uv (Python package manager) via multi-stage copy
-COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+COPY --from=uv /uv /usr/local/bin/uv
+
+# Install fzf from GitHub releases (newer than apt, includes built-in shell integration)
+ARG FZF_VERSION=0.67.0
+RUN ARCH=$(dpkg --print-architecture) && \
+  case "${ARCH}" in \
+    amd64) FZF_ARCH="linux_amd64" ;; \
+    arm64) FZF_ARCH="linux_arm64" ;; \
+    *) echo "Unsupported architecture: ${ARCH}" && exit 1 ;; \
+  esac && \
+  curl -fsSL "https://github.com/junegunn/fzf/releases/download/v${FZF_VERSION}/fzf-${FZF_VERSION}-${FZF_ARCH}.tar.gz" | tar -xz -C /usr/local/bin
 
 # Create directories and set ownership (combined for fewer layers)
 RUN mkdir -p /commandhistory /workspace /home/vscode/.claude /opt && \
@@ -88,12 +99,6 @@ RUN sh -c "$(curl -fsSL https://github.com/deluan/zsh-in-docker/releases/downloa
   -p git \
   -x
 
-# Download fzf shell integration (Ubuntu 24.04 package doesn't include these)
-ARG FZF_VERSION=0.44.1
-RUN mkdir -p /home/vscode/.fzf && \
-  curl -fsSL "https://raw.githubusercontent.com/junegunn/fzf/${FZF_VERSION}/shell/key-bindings.zsh" -o /home/vscode/.fzf/key-bindings.zsh && \
-  curl -fsSL "https://raw.githubusercontent.com/junegunn/fzf/${FZF_VERSION}/shell/completion.zsh" -o /home/vscode/.fzf/completion.zsh
-
 # Copy zsh configuration
 COPY --chown=vscode:vscode .zshrc /home/vscode/.zshrc.custom
 

devcontainer.json

@@ -10,8 +10,7 @@
     }
   },
   "features": {
-    "ghcr.io/devcontainers/features/github-cli:1": {},
-    "ghcr.io/tailscale/codespace/tailscale:1": {}
+    "ghcr.io/devcontainers/features/github-cli:1": {}
   },
   "runArgs": [
     "--cap-add=NET_ADMIN",

install.sh

@@ -76,6 +76,19 @@ check_devcontainer_cli() {
   fi
 }
 
+check_no_sys_admin() {
+  local workspace="${1:-.}"
+  local dc_json="$workspace/.devcontainer/devcontainer.json"
+  [[ -f "$dc_json" ]] || return 0
+  if jq -e \
+    '.runArgs[]? | select(test("SYS_ADMIN"))' \
+    "$dc_json" >/dev/null 2>&1; then
+    log_error "SYS_ADMIN capability detected in runArgs."
+    log_error "This defeats the read-only .devcontainer mount."
+    exit 1
+  fi
+}
+
 get_workspace_folder() {
   echo "${1:-$(pwd)}"
 }
@@ -101,19 +114,20 @@ extract_mounts_to_file() {
   custom_mounts=$(jq -c '
     .mounts // [] | map(
       select(
-        (startswith("source=claude-code-bashhistory-") | not) and
-        (startswith("source=claude-code-config-") | not) and
-        (startswith("source=claude-code-gh-") | not) and
-        (startswith("source=${localEnv:HOME}/.gitconfig,") | not) and
-        # Security: read-only .devcontainer mount prevents container escape on rebuild
-        (startswith("source=${localWorkspaceFolder}/.devcontainer,") | not)
+        (contains("target=/commandhistory,") | not) and
+        (contains("target=/home/vscode/.claude,") | not) and
+        (contains("target=/home/vscode/.config/gh,") | not) and
+        (contains("target=/home/vscode/.gitconfig,") | not) and
+        (contains("target=/workspace/.devcontainer,") | not)
       )
     ) | if length > 0 then . else empty end
   ' "$devcontainer_json" 2>/dev/null) || true
 
   if [[ -n "$custom_mounts" ]]; then
     echo "$custom_mounts" >"$temp_file"
     echo "$temp_file"
+  else
+    rm -f "$temp_file"
   fi
 }
 
@@ -207,6 +221,7 @@ cmd_up() {
   workspace_folder="$(get_workspace_folder "${1:-}")"
 
   check_devcontainer_cli
+  check_no_sys_admin "$workspace_folder"
   log_info "Starting devcontainer in $workspace_folder..."
 
   devcontainer up --workspace-folder "$workspace_folder"
@@ -218,6 +233,7 @@ cmd_rebuild() {
   workspace_folder="$(get_workspace_folder "${1:-}")"
 
   check_devcontainer_cli
+  check_no_sys_admin "$workspace_folder"
   log_info "Rebuilding devcontainer in $workspace_folder..."
 
   devcontainer up --workspace-folder "$workspace_folder" --remove-existing-container