fix: set correct $HOME in --oci mode when mount home = no

When `mount home = no` is set in `singularity.conf`, we still need to
set the correct value for `$HOME` in the container... we just don't
want to mount it.

Fixes sylabs/singularity#1783

Signed-off-by: Edita Kizinevic <edita.kizinevic@cern.ch>

e2e/config/oci.go

@@ -215,6 +215,17 @@ func (c configTests) ociConfigGlobal(t *testing.T) {
 			directiveValue: "no",
 			exit:           1,
 		},
+		// Verify that though mount is skipped, $HOME is still set correctly
+		// https://github.com/sylabs/singularity/issues/1783
+		{
+			name:           "MountHomeNoCorrectDir",
+			argv:           []string{archiveRef, "sh", "-c", "test $HOME == " + e2e.OCIUserProfile.ContainerUser(t).Dir},
+			profile:        e2e.OCIUserProfile,
+			cwd:            "/",
+			directive:      "mount home",
+			directiveValue: "no",
+			exit:           0,
+		},
 		{
 			name:           "MountHomeYes",
 			argv:           []string{archiveRef, "grep", e2e.OCIUserProfile.ContainerUser(t).Dir, "/proc/self/mountinfo"},

internal/pkg/runtime/launcher/oci/mounts_linux.go

@@ -265,13 +265,17 @@ func (l *Launcher) addSysMount(mounts *[]specs.Mount) error {
 	return nil
 }
 
-// addHomeMount adds a user home directory as a tmpfs mount. We are currently
-// emulating `--compat` / `--containall`, so the user must specifically bind in
-// their home directory from the host for it to be available.
+// addHomeMount adds a user home directory as a tmpfs mount, and sets the
+// container home directory. We are currently emulating `--compat` /
+// `--containall`, so the user must specifically bind in their home directory
+// from the host for it to be available.
 func (l *Launcher) addHomeMount(mounts *[]specs.Mount) error {
+	// If the $HOME mount is skipped by config need to still handle setting the
+	// correct $HOME dir, but just skip adding the mount.
+	skipMount := false
 	if !l.apptainerConf.MountHome {
 		sylog.Debugf("Skipping mount of $HOME due to apptainer.conf")
-		return nil
+		skipMount = true
 	}
 
 	// Get the host user's data
@@ -295,6 +299,10 @@ func (l *Launcher) addHomeMount(mounts *[]specs.Mount) error {
 			homeDest := homeSlice[1]
 			l.cfg.HomeDir = homeDest
 
+			if skipMount {
+				return nil
+			}
+
 			// Since the home dir is a bind-mount in this case, we don't have to mount a tmpfs directory for the in-container home dir, and we can just do the bind-mount & return.
 			return addBindMount(mounts, bind.Path{
 				Source:      homeSrc,
@@ -305,6 +313,11 @@ func (l *Launcher) addHomeMount(mounts *[]specs.Mount) error {
 		// If we're running in fake-root mode (and we haven't requested a custom home dir), we do need to create a tmpfs mount for the home dir, but it's a special case (because of its location & permissions), so we handle that here & return.
 		if l.cfg.Fakeroot {
 			l.cfg.HomeDir = "/root"
+
+			if skipMount {
+				return nil
+			}
+
 			*mounts = append(*mounts,
 				specs.Mount{
 					Destination: "/root",
@@ -325,6 +338,10 @@ func (l *Launcher) addHomeMount(mounts *[]specs.Mount) error {
 		l.cfg.HomeDir = pw.Dir
 	}
 
+	if skipMount {
+		return nil
+	}
+
 	// If we've not hit a special case (bind-mounted custom home dir, or fakeroot), then create a tmpfs mount as a home dir in the requested location (whether it's custom or not; by this point, l.cfg.HomeDir will reflect the right value).
 	*mounts = append(*mounts,
 		specs.Mount{