Add a setup hook for detecting $TMPDIR references in RPATHs and wrapper scripts

pkgs/build-support/setup-hooks/audit-tmpdir.sh

@@ -0,0 +1,41 @@
+# Check whether RPATHs or wrapper scripts contain references to
+# $TMPDIR. This is a serious security bug because it allows any user
+# to inject files into search paths of other users' processes.
+#
+# It might be better to have Nix scan build output for any occurrence
+# of $TMPDIR (which would also be good for reproducibility), but at
+# the moment that would produce too many spurious errors (e.g. debug
+# info or assertion messages that refer to $TMPDIR).
+
+fixupOutputHooks+=('if [ -z "$noAuditTmpdir" -a -e "$prefix" ]; then auditTmpdir "$prefix"; fi')
+
+auditTmpdir() {
+    local dir="$1"
+    [ -e "$dir" ] || return 0
+
+    header "checking for references to $TMPDIR in $dir..."
+
+    local i
+    while IFS= read -r -d $'\0' i; do
+        if [[ "$i" =~ .build-id ]]; then continue; fi
+
+        if isELF "$i"; then
+            if patchelf --print-rpath "$i" | grep -q -F "$TMPDIR"; then
+                echo "RPATH of binary $i contains a forbidden reference to $TMPDIR"
+                exit 1
+            fi
+        fi
+
+        if  isScript "$i"; then
+            if [ -e "$(dirname $i)/.$(basename $i)-wrapped" ]; then
+                if grep -q -F "$TMPDIR" "$i"; then
+                    echo "wrapper script $i contains a forbidden reference to $TMPDIR"
+                    exit 1
+                fi
+            fi
+        fi
+
+    done < <(find "$dir" -type f -print0)
+
+    stopNest
+}

pkgs/stdenv/generic/default.nix

@@ -94,6 +94,7 @@ let
       ../../build-support/setup-hooks/compress-man-pages.sh
       ../../build-support/setup-hooks/strip.sh
       ../../build-support/setup-hooks/patch-shebangs.sh
+      ../../build-support/setup-hooks/audit-tmpdir.sh
       ../../build-support/setup-hooks/multiple-outputs.sh
       ../../build-support/setup-hooks/move-sbin.sh
       ../../build-support/setup-hooks/move-lib64.sh

pkgs/stdenv/generic/setup.sh

@@ -199,6 +199,18 @@ isELF() {
     if [[ "$magic" =~ ELF ]]; then return 0; else return 1; fi
 }
 
+# Return success if the specified file is a script (i.e. starts with
+# "#!").
+isScript() {
+    local fn="$1"
+    local magic
+    if ! [ -x /bin/sh ]; then return 0; fi
+    exec {fd}< "$fn"
+    read -n 2 -u $fd magic
+    exec {fd}<&-
+    if [[ "$magic" =~ \#! ]]; then return 0; else return 1; fi
+}
+
 
 ######################################################################
 # Initialisation.