Pin GitHub Actions and narrow permissions (#892)

Author: anoadragon453

.github/workflows/ci.yaml

@@ -6,16 +6,24 @@ on:
   pull_request:
   workflow_dispatch:
 
+permissions: {}
+
 jobs:
   check-signoff:
     if: "github.event_name == 'pull_request'"
-    uses: "matrix-org/backend-meta/.github/workflows/sign-off.yml@v2"
+    permissions:
+      pull-requests: read
+    uses: matrix-org/backend-meta/.github/workflows/sign-off.yml@18beaf3c8e536108bd04d18e6c3dc40ba3931e28 # v2
 
   complement-internal:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     steps:
-      - uses: actions/checkout@v6.0.3 # Checkout complement
-      - uses: actions/setup-go@v6.5.0
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
+      - uses: actions/setup-go@924ae3a1cded613372ab5595356fb5720e22ba16 # v6.5.0
         with:
           go-version-file: go.mod
       - name: "Run internal Complement tests"
@@ -35,6 +43,8 @@ jobs:
   complement:
     name: Complement (${{ matrix.homeserver }})
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     strategy:
       fail-fast: false # ensure if synapse fails we keep running dendrite and vice-versa
       matrix:
@@ -54,9 +64,11 @@ jobs:
             timeout: 10m
 
     steps:
-      - uses: actions/checkout@v6.0.3 # Checkout complement
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
 
-      - uses: actions/setup-go@v6.5.0
+      - uses: actions/setup-go@924ae3a1cded613372ab5595356fb5720e22ba16 # v6.5.0
         with:
           go-version-file: go.mod
 
@@ -66,7 +78,7 @@ jobs:
       # servers which listen on random high numbered ports.
       - name: "Install Complement Dependencies"
         run: |
-          go install -v github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@latest
+          go install -v github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@v2.5.0
           mkdir .gotestfmt/github -p
           cp .ci/complement_package.gotpl .gotestfmt/github/package.gotpl
           gotestfmt -help

.github/workflows/zizmor.yaml

@@ -0,0 +1,24 @@
+# Taken from https://github.com/zizmorcore/zizmor-action/blob/f72bf176f67e8007f87b16d80f9880ece648aa65/README.md
+name: GitHub Actions Security Analysis with zizmor 🌈
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["**"]
+
+permissions: {}
+
+jobs:
+  zizmor:
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
+
+      - name: Run zizmor 🌈
+        uses: zizmorcore/zizmor-action@192e21d79ab29983730a13d1382995c2307fbcaa # v0.5.7