[1.0] Fix failure with rw bind mount of a ro fuse

.cirrus.yml

@@ -106,7 +106,7 @@ task:
       yum config-manager --set-enabled powertools
       ;;
     esac
-    yum install -y -q gcc git iptables jq glibc-static libseccomp-devel make criu
+    yum install -y -q gcc git iptables jq glibc-static libseccomp-devel make criu fuse-sshfs
     # install Go
     curl -fsSL "https://dl.google.com/go/go${GO_VERSION}.linux-amd64.tar.gz" | tar Cxz /usr/local
     # install bats
@@ -118,6 +118,12 @@ task:
     cd -
     # Add a user for rootless tests
     useradd -u2000 -m -d/home/rootless -s/bin/bash rootless
+    # Allow root and rootless itself to execute `ssh rootless@localhost` in tests/rootless.sh
+    ssh-keygen -t ecdsa -N "" -f /root/rootless.key
+    mkdir -m 0700 -p /home/rootless/.ssh
+    cp /root/rootless.key /home/rootless/.ssh/id_ecdsa
+    cat /root/rootless.key.pub >> /home/rootless/.ssh/authorized_keys
+    chown -R rootless.rootless /home/rootless
     # set PATH
     echo 'export PATH=/usr/local/go/bin:/usr/local/bin:$PATH' >> /root/.bashrc
     # Setup ssh localhost for terminal emulation (script -e did not work)

.github/workflows/test.yml

@@ -32,7 +32,7 @@ jobs:
         # criu repo
         sudo add-apt-repository -y ppa:criu/ppa
         # apt-add-repository runs apt update so we don't have to
-        sudo apt -q install libseccomp-dev criu
+        sudo apt -q install libseccomp-dev criu sshfs
 
     - name: install go ${{ matrix.go-version }}
       uses: actions/setup-go@v2
@@ -56,9 +56,10 @@ jobs:
       if: matrix.rootless == 'rootless'
       run: |
         sudo useradd -u2000 -m -d/home/rootless -s/bin/bash rootless
-        # Allow root to execute `ssh rootless@localhost` in tests/rootless.sh
+        # Allow root and rootless itself to execute `ssh rootless@localhost` in tests/rootless.sh
         ssh-keygen -t ecdsa -N "" -f $HOME/rootless.key
         sudo mkdir -m 0700 -p /home/rootless/.ssh
+        sudo cp $HOME/rootless.key /home/rootless/.ssh/id_ecdsa
         sudo cp $HOME/rootless.key.pub /home/rootless/.ssh/authorized_keys
         sudo chown -R rootless.rootless /home/rootless
 

Dockerfile

@@ -32,6 +32,7 @@ RUN echo 'deb https://download.opensuse.org/repositories/devel:/tools:/criu/Debi
         libseccomp2 \
         pkg-config \
         python-minimal \
+        sshfs \
         sudo \
         uidmap \
     && apt-get clean \

Vagrantfile.fedora34

@@ -21,7 +21,7 @@ Vagrant.configure("2") do |config|
 config exclude kernel,kernel-core
 config install_weak_deps false
 update
-install iptables gcc make golang-go glibc-static libseccomp-devel bats jq git-core criu
+install iptables gcc make golang-go glibc-static libseccomp-devel bats jq git-core criu fuse-sshfs
 ts run
 EOF
     done
@@ -30,9 +30,10 @@ EOF
     # Add a user for rootless tests
     useradd -u2000 -m -d/home/rootless -s/bin/bash rootless
 
-    # Allow root to execute `ssh rootless@localhost` in tests/rootless.sh
+    # Allow root and rootless itself to execute `ssh rootless@localhost` in tests/rootless.sh
     ssh-keygen -t ecdsa -N "" -f /root/rootless.key
     mkdir -m 0700 -p /home/rootless/.ssh
+    cp /root/rootless.key /home/rootless/.ssh/id_ecdsa
     cat /root/rootless.key.pub >> /home/rootless/.ssh/authorized_keys
     chown -R rootless.rootless /home/rootless
 

libcontainer/rootfs_linux.go

@@ -1035,7 +1035,22 @@ func writeSystemProperty(key, value string) error {
 
 func remount(m *configs.Mount, rootfs string) error {
 	return utils.WithProcfd(rootfs, m.Destination, func(procfd string) error {
-		return unix.Mount(m.Source, procfd, m.Device, uintptr(m.Flags|unix.MS_REMOUNT), "")
+		flags := uintptr(m.Flags | unix.MS_REMOUNT)
+		err := unix.Mount(m.Source, procfd, m.Device, flags, "")
+		if err == nil {
+			return nil
+		}
+		// Check if the source has ro flag...
+		var s unix.Statfs_t
+		if err := unix.Statfs(m.Source, &s); err != nil {
+			return &os.PathError{Op: "statfs", Path: m.Source, Err: err}
+		}
+		if s.Flags&unix.MS_RDONLY != unix.MS_RDONLY {
+			return err
+		}
+		// ... and retry the mount with ro flag set.
+		flags |= unix.MS_RDONLY
+		return unix.Mount(m.Source, procfd, m.Device, flags, "")
 	})
 }
 

tests/integration/mounts_sshfs.bats

@@ -0,0 +1,40 @@
+#!/usr/bin/env bats
+
+load helpers
+
+function setup() {
+	# Create a ro fuse-sshfs mount; skip the test if it's not working.
+	local sshfs="sshfs
+		-o UserKnownHostsFile=/dev/null
+		-o StrictHostKeyChecking=no
+		-o PasswordAuthentication=no"
+
+	DIR="$BATS_RUN_TMPDIR/fuse-sshfs"
+	mkdir -p "$DIR"
+
+	if ! $sshfs -o ro rootless@localhost: "$DIR"; then
+		skip "test requires working sshfs mounts"
+	fi
+
+	setup_hello
+}
+
+function teardown() {
+	# New distros (Fedora 35) do not have fusermount installed
+	# as a dependency of fuse-sshfs, and good ol' umount works.
+	fusermount -u "$DIR" || umount "$DIR"
+
+	teardown_bundle
+}
+
+@test "runc run [rw bind mount of a ro fuse sshfs mount]" {
+	update_config '	  .mounts += [{
+					type: "bind",
+					source: "'"$DIR"'",
+					destination: "/mnt",
+					options: ["rw", "rprivate", "nosuid", "nodev", "rbind"]
+				}]'
+
+	runc run test_busybox
+	[ "$status" -eq 0 ]
+}