Fallback to SUDO_USER when running on NFS.

When running on NFS, the root user may not be able to access ~/.ssh and
~/.gitconfig, so it is necessary to fallback to SUDO_USER to access these
files.

To discourage users from using NFS homedirs, print warnings every time
cros_sdk is run with an NFS homedir.

BUG=chromium-os:36783
TEST=Try cros_sdk --replace and cros_sdk with and without NFS homedirs.

Change-Id: I4cdbceca485d3491656d6f743814da4ebcdd75ad
Reviewed-on: https://gerrit.chromium.org/gerrit/38953
Commit-Ready: David James <davidjames@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>

common.sh

@@ -421,6 +421,16 @@ setup_board_warning() {
   echo
 }
 
+is_nfs() {
+  [ "$(stat -f -L -c %T "$1")" = "nfs" ]
+}
+
+warn_if_nfs() {
+  if is_nfs "$1"; then
+    warn "$1 is on NFS. This is unsupported."
+  fi
+}
+
 # Enter a chroot and restart the current script if needed
 restart_in_chroot_if_needed() {
   # NB:  Pass in ARGV:  restart_in_chroot_if_needed "$@"
@@ -546,6 +556,13 @@ user_clobber() {
   install -m644 -o ${SUDO_UID} -g ${SUDO_GID} /dev/stdin "$@"
 }
 
+# Copies the specified file owned by the user to the specified location.
+# If the copy fails as root (e.g. due to root_squash and NFS), retry the copy
+# with the user's account before failing.
+user_cp() {
+  cp -p "$@" 2>/dev/null || sudo -u ${SUDO_USER} -- cp -p "$@"
+}
+
 # Appends stdin to the given file name as the sudo user.
 #
 # $1 - The output file name.

sdk_lib/enter_chroot.sh

@@ -139,7 +139,7 @@ copy_ssh_config() {
   local filter
   local option
 
-  if [ ! -f "${sshc}" ]; then
+  if ! user_cp "${sshc}" "${chroot_ssh_dir}/config.orig" 2>/dev/null; then
     return # Nothing to copy.
   fi
 
@@ -152,7 +152,7 @@ copy_ssh_config() {
     fi
   done
 
-  sed "/^.*\(${filter}\).*$/d" "${sshc}" | \
+  sed "/^.*\(${filter}\).*$/d" "${chroot_ssh_dir}/config.orig" | \
     user_clobber "${chroot_ssh_dir}/config"
 }
 
@@ -285,9 +285,15 @@ setup_env() {
       if [ -n "${SSH_AUTH_SOCK}" -a -d "${SUDO_HOME}/.ssh" ]; then
         TARGET_DIR="${FLAGS_chroot}/home/${SUDO_USER}/.ssh"
         user_mkdir "${TARGET_DIR}"
-        # Ignore errors as some people won't have these files to copy.
-        cp -p "${SUDO_HOME}"/.ssh/{known_hosts,*.pub} "${TARGET_DIR}/" \
-          2>/dev/null || :
+        (
+          # Only copy ~/.ssh/{known_hosts,*.pub} if they exist. Since we set
+          # nullglob, this needs to happen within a subshell.
+          shopt -s nullglob
+          files=("${SUDO_HOME}"/.ssh/{known_hosts,*.pub})
+          if [[ ${#files[@]} -gt 0 ]]; then
+            user_cp "${files[@]}" "${TARGET_DIR}/"
+          fi
+        )
         copy_ssh_config "${TARGET_DIR}"
         chown -R ${SUDO_UID}:${SUDO_GID} "${TARGET_DIR}"
 

sdk_lib/make_chroot.sh

@@ -301,7 +301,7 @@ EOF
      # Copy .gitconfig into chroot so repo and git can be used from inside.
      # This is required for repo to work since it validates the email address.
      echo "Copying ~/.gitconfig into chroot"
-     cp -p "${SUDO_HOME}/.gitconfig" "$FLAGS_chroot/home/${SUDO_USER}/"
+     user_cp "${SUDO_HOME}/.gitconfig" "$FLAGS_chroot/home/${SUDO_USER}/"
    fi
 
    # If the user didn't set up their username in their gitconfig, look
@@ -513,3 +513,5 @@ delete the chroot cleanly, use:
 $ cros_sdk --delete $CHROOT_EXAMPLE_OPT
 
 EOF
+
+warn_if_nfs "${SUDO_HOME}"