Handle RUN --mount with relative targets and no configured workdir

When the target location of a RUN --mount is specified as a relative
path, we normally try to convert it to an absolute path by combining it
with the currently-configured working directory.  If there is no such
value, though, the result is still not an absolute path.  Work around
this by using "/" when the configured working directory is "".

Set this field in the `runMountInfo` struct on FreeBSD, as we already
did on Linux.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

internal/volumes/volumes.go

@@ -531,6 +531,7 @@ func GetVolumes(ctx *types.SystemContext, store storage.Store, volumes []string,
 // getMounts takes user-provided input from the --mount flag and creates OCI
 // spec mounts.
 // buildah run --mount type=bind,src=/etc/resolv.conf,target=/etc/resolv.conf ...
+// buildah run --mount type=cache,target=/var/cache ...
 // buildah run --mount type=tmpfs,target=/dev/shm ...
 //
 // If this function succeeds, the caller must unlock the returned *lockfile.LockFile s if any (when??).
@@ -590,7 +591,7 @@ func getMounts(ctx *types.SystemContext, store storage.Store, mounts []string, c
 			}
 			finalMounts[mount.Destination] = mount
 		case TypeTmpfs:
-			mount, err := GetTmpfsMount(tokens)
+			mount, err := GetTmpfsMount(tokens, workDir)
 			if err != nil {
 				return nil, mountedImages, nil, err
 			}
@@ -608,7 +609,7 @@ func getMounts(ctx *types.SystemContext, store storage.Store, mounts []string, c
 }
 
 // GetTmpfsMount parses a single tmpfs mount entry from the --mount flag
-func GetTmpfsMount(args []string) (specs.Mount, error) {
+func GetTmpfsMount(args []string, workDir string) (specs.Mount, error) {
 	newMount := specs.Mount{
 		Type:   TypeTmpfs,
 		Source: TypeTmpfs,
@@ -646,10 +647,14 @@ func GetTmpfsMount(args []string) (specs.Mount, error) {
 			if !hasArgValue {
 				return newMount, fmt.Errorf("%v: %w", argName, errBadOptionArg)
 			}
-			if err := parse.ValidateVolumeCtrDir(argValue); err != nil {
+			targetPath := argValue
+			if !path.IsAbs(targetPath) {
+				targetPath = filepath.Join(workDir, targetPath)
+			}
+			if err := parse.ValidateVolumeCtrDir(targetPath); err != nil {
 				return newMount, err
 			}
-			newMount.Destination = argValue
+			newMount.Destination = targetPath
 			setDest = true
 		default:
 			return newMount, fmt.Errorf("%v: %w", argName, errBadMntOption)

run_common.go

@@ -1605,7 +1605,7 @@ func (b *Builder) runSetupRunMounts(mountPoint string, mounts []string, sources
 				mountImages = append(mountImages, image)
 			}
 		case "tmpfs":
-			mountSpec, err = b.getTmpfsMount(tokens, idMaps)
+			mountSpec, err = b.getTmpfsMount(tokens, idMaps, sources.WorkDir)
 			if err != nil {
 				return nil, nil, err
 			}
@@ -1665,9 +1665,9 @@ func (b *Builder) getBindMount(tokens []string, context *imageTypes.SystemContex
 	return &volumes[0], image, nil
 }
 
-func (b *Builder) getTmpfsMount(tokens []string, idMaps IDMaps) (*specs.Mount, error) {
+func (b *Builder) getTmpfsMount(tokens []string, idMaps IDMaps, workDir string) (*specs.Mount, error) {
 	var optionMounts []specs.Mount
-	mount, err := volumes.GetTmpfsMount(tokens)
+	mount, err := volumes.GetTmpfsMount(tokens, workDir)
 	if err != nil {
 		return nil, err
 	}

run_freebsd.go

@@ -124,10 +124,16 @@ func (b *Builder) Run(command []string, options RunOptions) error {
 		return err
 	}
 
+	workDir := b.WorkDir()
 	if options.WorkingDir != "" {
 		g.SetProcessCwd(options.WorkingDir)
+		workDir = options.WorkingDir
 	} else if b.WorkDir() != "" {
 		g.SetProcessCwd(b.WorkDir())
+		workDir = b.WorkDir()
+	}
+	if workDir == "" {
+		workDir = string(os.PathSeparator)
 	}
 	mountPoint, err := b.Mount(b.MountLabel)
 	if err != nil {
@@ -249,6 +255,7 @@ func (b *Builder) Run(command []string, options RunOptions) error {
 	}
 
 	runMountInfo := runMountInfo{
+		WorkDir:          workDir,
 		ContextDir:       options.ContextDir,
 		Secrets:          options.Secrets,
 		SSHSources:       options.SSHSources,

run_linux.go

@@ -237,6 +237,10 @@ func (b *Builder) Run(command []string, options RunOptions) error {
 		workDir = options.WorkingDir
 	} else if b.WorkDir() != "" {
 		g.SetProcessCwd(b.WorkDir())
+		workDir = b.WorkDir()
+	}
+	if workDir == "" {
+		workDir = string(os.PathSeparator)
 	}
 	setupSelinux(g, b.ProcessLabel, b.MountLabel)
 	mountPoint, err := b.Mount(b.MountLabel)

tests/bud.bats

@@ -7017,3 +7017,17 @@ EOF
   run_buildah 1 build --security-opt label=disable --build-context testbuild=${TEST_SCRATCH_DIR}/cve20249675/ --no-cache ${TEST_SCRATCH_DIR}/cve20249675/
   expect_output --substring "cat: can't open '/var/tmp/file.txt': No such file or directory"
 }
+
+@test "build-mounts-implicit-workdir" {
+  base=busybox
+  _prefetch $base
+  run_buildah inspect --format '{{.Docker.Config.WorkingDir}}' --type=image $base
+  expect_output "" "test base image needs to not have a default working directory defined in its configuration"
+  # check that the target for a bind mount can be specified as a relative path even when there's no WorkingDir defined for it to be relative to
+  echo FROM $base > ${TEST_SCRATCH_DIR}/Containerfile
+  echo RUN --mount=type=bind,src=Containerfile,target=Containerfile test -s Containerfile >> ${TEST_SCRATCH_DIR}/Containerfile
+  echo RUN --mount=type=cache,id=cash,target=cachesubdir truncate -s 1024 cachesubdir/cachefile >> ${TEST_SCRATCH_DIR}/Containerfile
+  echo RUN --mount=type=cache,id=cash,target=cachesubdir2 test -s cachesubdir2/cachefile >> ${TEST_SCRATCH_DIR}/Containerfile
+  echo RUN --mount=type=tmpfs,target=tmpfssubdir test '`stat -f -c %i .`' '!=' '`stat -f -c %i tmpfssubdir`' >> ${TEST_SCRATCH_DIR}/Containerfile
+  run_buildah build --security-opt label=disable ${TEST_SCRATCH_DIR}
+}