Fix underlay bind issue when the destination is a symlink

pointing to a relative/absolute path.

e2e/actions/actions.go

@@ -1518,6 +1518,7 @@ func E2ETests(env e2e.TestEnv) func(*testing.T) {
 		"issue 4587":            c.issue4587,           // https://github.com/sylabs/singularity/issues/4587
 		"issue 4755":            c.issue4755,           // https://github.com/sylabs/singularity/issues/4755
 		"issue 4768":            c.issue4768,           // https://github.com/sylabs/singularity/issues/4768
+		"issue 4797":            c.issue4797,           // https://github.com/sylabs/singularity/issues/4797
 		"network":               c.actionNetwork,       // test basic networking
 		"binds":                 c.actionBinds,         // test various binds
 		"exit and signals":      c.exitSignals,         // test exit and signals propagation

e2e/actions/regressions.go

@@ -124,3 +124,51 @@ func (c actionTests) issue4768(t *testing.T) {
 		),
 	)
 }
+
+// Check that underlay layer handle relative/absolute symlinks
+// when those are bind mount points.
+func (c actionTests) issue4797(t *testing.T) {
+	e2e.EnsureImage(t, c.env)
+
+	// /etc/relative-slink in the image point to ../usr/share/zoneinfo/Etc/UTC
+	// /etc/absolute-slink in the image point to /usr/share/zoneinfo/Etc/UTC
+	tests := []struct {
+		name string
+		args []string
+		exit int
+	}{
+		{
+			// check /usr/bin presence in the container
+			name: "RelativeUsrBin",
+			args: []string{"--bind", "/etc/passwd:/etc/relative-slink", c.env.ImagePath, "test", "-d", "/usr/bin"},
+			exit: 0,
+		},
+		{
+			// check /usr/share/zoneinfo/Etc/UTC presence in the container
+			name: "RelativeUTC",
+			args: []string{"--bind", "/etc/passwd:/etc/relative-slink", c.env.ImagePath, "test", "-f", "/usr/share/zoneinfo/Etc/UTC"},
+			exit: 0,
+		},
+		{
+			name: "AbsoluteUsrBin",
+			args: []string{"--bind", "/etc/passwd:/etc/absolute-slink", c.env.ImagePath, "test", "-d", "/usr/bin"},
+			exit: 0,
+		},
+		{
+			name: "AbsoluteUTC",
+			args: []string{"--bind", "/etc/passwd:/etc/absolute-slink", c.env.ImagePath, "test", "-f", "/usr/share/zoneinfo/Etc/UTC"},
+			exit: 0,
+		},
+	}
+
+	for _, tt := range tests {
+		c.env.RunSingularity(
+			t,
+			e2e.AsSubtest(tt.name),
+			e2e.WithProfile(e2e.UserNamespaceProfile),
+			e2e.WithCommand("exec"),
+			e2e.WithArgs(tt.args...),
+			e2e.ExpectExit(tt.exit),
+		)
+	}
+}

e2e/testdata/Singularity

@@ -74,5 +74,9 @@ export HELLOTHISIS
     mkdir /madness
     ln -s /madness /var/etc/madness
 
+    # for underlay regression tests
+    ln -s ../usr/share/zoneinfo/Etc/UTC /etc/relative-slink
+    ln -s /usr/share/zoneinfo/Etc/UTC /etc/absolute-slink
+
 %test
     exec "$@"

internal/pkg/util/fs/layout/layer/underlay/underlay_linux.go

@@ -96,25 +96,25 @@ func (u *Underlay) createLayer(rootFsPath string, system *mount.System) error {
 				sylog.Warningf("skipping mount of %s: %s", point.Source, err)
 				continue
 			}
-			dst = filepath.Join(underlayDir, dst)
-			if _, err := u.session.GetPath(dst); err == nil {
+			underlayDst := filepath.Join(underlayDir, dst)
+			if _, err := u.session.GetPath(underlayDst); err == nil {
 				continue
 			}
 			switch st.Mode & syscall.S_IFMT {
 			case syscall.S_IFDIR:
-				if err := u.session.AddDir(dst); err != nil {
+				if err := u.session.AddDir(underlayDst); err != nil {
 					return err
 				}
 			default:
-				if err := u.session.AddFile(dst, nil); err != nil {
+				if err := u.session.AddFile(underlayDst, nil); err != nil {
 					return err
 				}
 			}
 			createdPath = append(
 				createdPath,
 				pathLen{
-					path: point.Destination,
-					len:  uint16(strings.Count(point.Destination, "/")),
+					path: dst,
+					len:  uint16(strings.Count(dst, "/")),
 				},
 			)
 		}
@@ -137,14 +137,13 @@ func (u *Underlay) createLayer(rootFsPath string, system *mount.System) error {
 						return err
 					}
 				}
-				dir := fs.EvalRelative(p, rootFsPath)
 				// if the directory is overrided by a bind mount we won't
 				// need to duplicate the container image directory
-				if _, ok := destinations[dir]; ok {
+				if _, ok := destinations[p]; ok {
 					continue
 				}
 				// directory not overrided, duplicate it
-				if err := u.duplicateDir(dir, system, pl.path); err != nil {
+				if err := u.duplicateDir(p, system, pl.path); err != nil {
 					return err
 				}
 			}