prevent using same file for input tar and output tar

Signed-off-by: Avi Deitcher <avi@deitcher.net>

src/cmd/linuxkit/build.go

@@ -205,8 +205,10 @@ The generated image can be in one of multiple formats which can be run on variou
 				return nil
 			}
 
-			var tf *os.File
-			var w io.Writer
+			var (
+				tf *os.File
+				w  io.Writer
+			)
 			if outfile != nil {
 				w = outfile
 			} else {
@@ -216,6 +218,9 @@ The generated image can be in one of multiple formats which can be run on variou
 				defer os.Remove(tf.Name())
 				w = tf
 			}
+			if inputTar != "" && inputTar == outputFile {
+				return fmt.Errorf("input-tar and output file cannot be the same")
+			}
 
 			// this is a weird interface, but currently only streamable types can have additional files
 			// need to split up the base tarball outputs from the secondary stages

src/cmd/linuxkit/moby/build.go

@@ -139,34 +139,23 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 	}
 	var (
 		oldConfig *Moby
-		tmpfile   *os.File
+		in        *os.File
 		err       error
 	)
 	if metadataLocation != "" && opts.InputTar != "" {
 		// copy the file over, in case it ends up being the same output
-		tmpfile, err = os.CreateTemp("", "linuxkit-input.tar")
-		if err != nil {
-			return fmt.Errorf("failed to create temporary file: %w", err)
-		}
-		defer tmpfile.Close()
-		in, err := os.Open(opts.InputTar)
+		in, err = os.Open(opts.InputTar)
 		if err != nil {
 			return fmt.Errorf("failed to open input tar: %w", err)
 		}
-		if _, err := io.Copy(tmpfile, in); err != nil {
-			return fmt.Errorf("failed to copy input tar: %w", err)
-		}
-		if err := in.Close(); err != nil {
-			return fmt.Errorf("failed to close input file: %w", err)
-		}
-		if _, err := tmpfile.Seek(0, 0); err != nil {
+		defer in.Close()
+		if _, err := in.Seek(0, 0); err != nil {
 			return fmt.Errorf("failed to seek to beginning of tmpfile: %w", err)
 		}
-		// for efficiency, get the trimmed metadata path in advance
-		tmpTar := tar.NewReader(tmpfile)
 		// read the tar until we find the metadata file
+		inputTarReader := tar.NewReader(in)
 		for {
-			hdr, err := tmpTar.Next()
+			hdr, err := inputTarReader.Next()
 			if err == io.EOF {
 				break
 			}
@@ -175,7 +164,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 			}
 			if strings.TrimPrefix(hdr.Name, "/") == metadataLocation {
 				buf := new(bytes.Buffer)
-				if _, err := buf.ReadFrom(tmpTar); err != nil {
+				if _, err := buf.ReadFrom(inputTarReader); err != nil {
 					return fmt.Errorf("failed to read metadata file from input tar: %w", err)
 				}
 				config, err := NewConfig(buf.Bytes(), nil)
@@ -217,7 +206,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 		// first check if the existing one had it
 		//if config != nil && len(oldConfig.initRefs) > index+1 && oldConfig.initRefs[index].String() == image {
 		if oldConfig != nil && oldConfig.Kernel.ref != nil && oldConfig.Kernel.ref.String() == m.Kernel.ref.String() {
-			if err := extractPackageFilesFromTar(tmpfile, iw, m.Kernel.ref.String(), "kernel"); err != nil {
+			if err := extractPackageFilesFromTar(in, iw, m.Kernel.ref.String(), "kernel"); err != nil {
 				return err
 			}
 		} else {
@@ -242,7 +231,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 	apkTar := newAPKTarWriter(iw, "init")
 	for i, ii := range m.initRefs {
 		if oldConfig != nil && len(oldConfig.initRefs) > i && oldConfig.initRefs[i].String() == ii.String() {
-			if err := extractPackageFilesFromTar(tmpfile, apkTar, ii.String(), fmt.Sprintf("init[%d]", i)); err != nil {
+			if err := extractPackageFilesFromTar(in, apkTar, ii.String(), fmt.Sprintf("init[%d]", i)); err != nil {
 				return err
 			}
 		} else {
@@ -262,7 +251,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 	}
 	for i, image := range m.Onboot {
 		if oldConfig != nil && len(oldConfig.Onboot) > i && oldConfig.Onboot[i].Equal(image) {
-			if err := extractPackageFilesFromTar(tmpfile, iw, image.Image, fmt.Sprintf("onboot[%d]", i)); err != nil {
+			if err := extractPackageFilesFromTar(in, iw, image.Image, fmt.Sprintf("onboot[%d]", i)); err != nil {
 				return err
 			}
 		} else {
@@ -278,7 +267,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 	}
 	for i, image := range m.Onshutdown {
 		if oldConfig != nil && len(oldConfig.Onshutdown) > i && oldConfig.Onshutdown[i].Equal(image) {
-			if err := extractPackageFilesFromTar(tmpfile, iw, image.Image, fmt.Sprintf("onshutdown[%d]", i)); err != nil {
+			if err := extractPackageFilesFromTar(in, iw, image.Image, fmt.Sprintf("onshutdown[%d]", i)); err != nil {
 				return err
 			}
 		} else {
@@ -294,7 +283,7 @@ func Build(m Moby, w io.Writer, opts BuildOpts) error {
 	}
 	for i, image := range m.Services {
 		if oldConfig != nil && len(oldConfig.Services) > i && oldConfig.Services[i].Equal(image) {
-			if err := extractPackageFilesFromTar(tmpfile, iw, image.Image, fmt.Sprintf("services[%d]", i)); err != nil {
+			if err := extractPackageFilesFromTar(in, iw, image.Image, fmt.Sprintf("services[%d]", i)); err != nil {
 				return err
 			}
 		} else {

test/cases/000_build/060_input_tar/000_build/test.sh

@@ -8,7 +8,7 @@ set -e
 #. "${RT_LIB}"
 . "${RT_PROJECT_ROOT}/_lib/lib.sh"
 
-NAME=check
+NAME=check_input_tar
 
 clean_up() {
 	rm -f ${NAME}-*.tar

test/cases/000_build/060_input_tar/010_same_filename/test.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+# SUMMARY: Check that tar output format build is reproducible after leveraging input tar
+# LABELS:
+
+set -e
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+NAME=check_input_tar_conflict_filename
+
+clean_up() {
+	rm -f ${NAME}-*.tar
+}
+
+trap clean_up EXIT
+
+logfile=$(mktemp)
+
+# do not include the sbom, because the SBoM unique IDs per file/package are *not* deterministic,
+# (currently based upon syft), and thus will make the file non-reproducible
+
+# the first one should build normally without a problem
+linuxkit build --no-sbom --format tar --o "${NAME}-1.tar" ./test.yml
+
+# second one should fail because the input tar has the same filename as the output tar
+set +e
+linuxkit build -v --no-sbom --format tar --input-tar "${NAME}-1.tar" --o "${NAME}-1.tar" ./test.yml 2>&1
+ret="$?"
+set -e
+
+if [ "$ret" -eq 0 ]; then
+	echo "Expected the build to fail, but it succeeded"
+	exit 1
+fi
+
+exit 0

test/cases/000_build/060_input_tar/010_same_filename/test.yml

@@ -0,0 +1,37 @@
+kernel:
+  image: linuxkit/kernel:6.6.13
+  cmdline: "console=tty0 console=ttyS0 console=ttyAMA0"
+init:
+  - linuxkit/init:45a1ad5919f0b6acf0f0cf730e9434abfae11fe6
+  - linuxkit/runc:6062483d748609d505f2bcde4e52ee64a3329f5f
+  - linuxkit/containerd:e7a92d9f3282039eac5fb1b07cac2b8664cbf0ad
+onboot:
+  - name: sysctl
+    image: linuxkit/sysctl:5a374e4bf3e5a7deeacff6571d0f30f7ea8f56db
+  - name: dhcpcd
+    image: linuxkit/dhcpcd:e9e3580f2de00e73e7b316a007186d22fea056ee
+    command: ["/sbin/dhcpcd", "--nobackground", "-f", "/dhcpcd.conf", "-1"]
+onshutdown:
+  - name: shutdown
+    image: busybox:latest
+    command: ["/bin/echo", "so long and thanks for all the fish"]
+services:
+  - name: getty
+    image: linuxkit/getty:5d86a2ce2d890c14ab66b13638dcadf74f29218b
+    env:
+     - INSECURE=true
+  - name: rngd
+    image: linuxkit/rngd:cdb919e4aee49fed0bf6075f0a104037cba83c39
+  - name: nginx
+    image: nginx:1.19.5-alpine
+    capabilities:
+     - CAP_NET_BIND_SERVICE
+     - CAP_CHOWN
+     - CAP_SETUID
+     - CAP_SETGID
+     - CAP_DAC_OVERRIDE
+    binds:
+     - /etc/resolv.conf:/etc/resolv.conf
+files:
+  - path: etc/linuxkit-config
+    metadata: yaml