ccon: Create mount target files/directories based on source stat

Avoid:

  mount("/some/source/file", "/some/target/file", NULL, MS_BIND, NULL) = -1 ENOTDIR (Not a directory)

by creating target *files* (instead of directories) in those cases.

README.md

@@ -348,9 +348,12 @@ processes inside a user namespace.
 
 If they don't start with a slash, **`source`** and **`target`** are
 interpreted as paths relative to ccon's [current working
-directory][getcwd.3].  If **`target`** does not exist, ccon will
-attempt to create it by calling [`mkdir`][mkdir.3p], making multiple
-calls if necessary.
+directory][getcwd.3].
+
+If **`target`** does not exist, ccon will attempt to create it by
+calling [`mkdir`][mkdir.3p], making multiple calls if necessary.  If
+**`source`** is set to a non-directory and **`target`** does not exit,
+ccon will create an empty file at **`target`** to mount over.
 
 In addition to the usual types supported by [`mount`][mount.2], ccon
 supports a `pivot-root` **`type`** that invokes the

ccon.c

@@ -123,6 +123,7 @@ static char **json_array_of_strings_value(json_t * array);
 static int close_pipe(int pipe_fd[]);
 static int splice_pseudoterminal_master(int *master, int *slave);
 static int mkdir_all(const char *path, mode_t mode);
+static int mkfile_all(const char *path, mode_t dir_mode, mode_t file_mode);
 
 int main(int argc, char **argv)
 {
@@ -2137,12 +2138,13 @@ static int get_mount_flag(const char *name, unsigned long *flag)
 
 static int handle_mounts(json_t * config)
 {
+	struct stat buf;
 	json_t *namespaces, *mt_ns, *mounts, *mt, *v1, *v2;
 	const char *source, *target, *type, *data, *flag;
 	char cwd[MAX_PATH], full_source[MAX_PATH], full_target[MAX_PATH];
 	unsigned long flags, f;
 	size_t i, j;
-	int size;
+	int size, mkdir;
 
 	namespaces = json_object_get(config, "namespaces");
 	if (!namespaces) {
@@ -2253,7 +2255,19 @@ static int handle_mounts(json_t * config)
 				return 1;
 			}
 		} else {
-			if (mkdir_all(target, 0777) == -1) {
+			mkdir = 1;
+			if (source) {
+				if (stat(source, &buf) == -1) {
+					PERROR("stat");
+					return 1;
+				}
+				mkdir = S_ISDIR(buf.st_mode);
+			}
+			if (mkdir) {
+				if (mkdir_all(target, 0777) == -1) {
+					return 1;
+				}
+			} else if (mkfile_all(target, 0777, 0666) == -1) {
 				return 1;
 			}
 
@@ -2620,7 +2634,7 @@ static int mkdir_all(const char *path, mode_t mode)
 				err = -1;
 				goto cleanup;
 			}
-			LOG("create directory %s\n", path);;
+			LOG("create directory %s\n", path);
 			if (mkdir(path, mode) == -1) {
 				PERROR("mkdir");
 				err = -1;
@@ -2639,3 +2653,37 @@ static int mkdir_all(const char *path, mode_t mode)
 	}
 	return err;
 }
+
+static int mkfile_all(const char *path, mode_t dir_mode, mode_t file_mode)
+{
+	char *path_copy = NULL, *dir = NULL;
+	int fd = -1, err = 0;
+
+	path_copy = strdup(path);
+	if (path_copy == NULL) {
+		PERROR("strdup");
+		err = -1;
+		goto cleanup;
+	}
+	dir = dirname(path_copy);
+	if (mkdir_all(dir, dir_mode) == -1) {
+		err = -1;
+		goto cleanup;
+	}
+	LOG("create file %s\n", path);
+	fd = open(path, O_CREAT | O_RDONLY, file_mode);
+	if (fd == -1) {
+		PERROR("mkdir_all open");
+	}
+
+ cleanup:
+	if (fd >= 0) {
+		if (close(fd) == -1) {
+			PERROR("close mkdir_all descriptor");
+		}
+	}
+	if (path_copy != NULL) {
+		free(path_copy);
+	}
+	return err;
+}

test/t2002-mount-namespace.t

@@ -156,4 +156,51 @@ test_expect_success BUSYBOX,ID 'Test mount namespace creates destination directo
 	test_cmp expected actual
 "
 
+test_expect_success BUSYBOX,ID 'Test mount namespace creates destination files' "
+	mkdir -p rootfs &&
+	ccon --verbose --config-string '{
+		  \"version\": \"0.5.0\",
+		  \"namespaces\": {
+		    \"user\": {
+		      \"setgroups\": false,
+		      \"uidMappings\": [
+		        {
+		          \"containerID\": 0,
+		          \"hostID\": $(id -u),
+		          \"size\": 1
+		        }
+		      ],
+		      \"gidMappings\": [
+		        {
+		          \"containerID\": 0,
+		          \"hostID\": $(id -u),
+		          \"size\": 1
+		        }
+		      ]
+		    },
+		    \"mount\": {
+		      \"mounts\": [
+		        {
+		          \"target\": \"/tmp/\",
+		          \"type\": \"tmpfs\"
+		        },
+		        {
+		          \"source\": \"/bin/busybox\",
+		          \"target\": \"/tmp/a/b/c\",
+		          \"flags\": [
+		            \"MS_BIND\"
+		          ]
+		        }
+		      ]
+		    }
+		  },
+		  \"process\": {
+		    \"args\": [\"/bin/busybox\", \"ls\", \"/tmp/a/b\"],
+		    \"host\": true
+		  }
+		}' >actual &&
+	echo c >expected &&
+	test_cmp expected actual
+"
+
 test_done