criu: Throw error when parent path is provided but invalid

In image dump directory, there are 2 parent symlink error cases:
- Parent symlink does not exist
- Parent symlink exists but points to invalid target

At the moment, 2 cases are handled exactly the same (do full dump). However, while
the first case happen when parent path is not provided, the second one is likely
user's mistake when provides invalid parent path.

So we throw an error in the latter case instead of performing the full dump.

Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>

criu/image.c

@@ -149,8 +149,7 @@ InventoryEntry *get_parent_inventory(void)
 	InventoryEntry *ie;
 	int dir;
 
-	dir = openat(get_service_fd(IMG_FD_OFF), CR_PARENT_LINK, O_RDONLY);
-	if (dir == -1) {
+	if (open_parent(get_service_fd(IMG_FD_OFF), &dir)) {
 		/*
 		 * We print the warning below to be notified that we had some
 		 * unexpected problem on open. For instance we have a parent
@@ -158,10 +157,11 @@ InventoryEntry *get_parent_inventory(void)
 		 * when also having no parent directory is an expected case of
 		 * first dump iteration.
 		 */
-		if (errno != ENOENT)
-			pr_warn("Failed to open parent directory\n");
+		pr_warn("Failed to open parent directory\n");
 		return NULL;
 	}
+	if (dir < 0)
+		return NULL;
 
 	img = open_image_at(dir, CR_FD_INVENTORY, O_RSTR);
 	if (!img) {
@@ -561,6 +561,11 @@ int open_image_dir(char *dir, int mode)
 		if (img_streamer_init(dir, mode) < 0)
 			goto err;
 	} else if (opts.img_parent) {
+		if (faccessat(fd, opts.img_parent, R_OK, 0)) {
+			pr_perror("Invalid parent image directory provided");
+			goto err;
+		}
+
 		ret = symlinkat(opts.img_parent, fd, CR_PARENT_LINK);
 		if (ret < 0 && errno != EEXIST) {
 			pr_perror("Can't link parent snapshot");
@@ -586,6 +591,24 @@ void close_image_dir(void)
 	close_service_fd(IMG_FD_OFF);
 }
 
+int open_parent(int dfd, int *pfd)
+{
+	*pfd = -1;
+	/* Check if the parent symlink exists */
+	if (faccessat(dfd, CR_PARENT_LINK, F_OK, AT_SYMLINK_NOFOLLOW) && errno == ENOENT) {
+		pr_debug("No parent images directory provided\n");
+		return 0;
+	}
+
+	*pfd = openat(dfd, CR_PARENT_LINK, O_RDONLY);
+	if (*pfd < 0) {
+		pr_perror("Can't open parent path");
+		return -1;
+	}
+
+	return 0;
+}
+
 static unsigned long page_ids = 1;
 
 void up_page_ids_base(void)

criu/include/image.h

@@ -147,6 +147,12 @@ extern off_t img_raw_size(struct cr_img *img);
 
 extern int open_image_dir(char *dir, int mode);
 extern void close_image_dir(void);
+/*
+ * Return -1 -- parent symlink points to invalid target
+ * Return 0 && pfd < 0 -- parent symlink does not exist
+ * Return 0 && pfd >= 0 -- opened
+ */
+extern int open_parent(int dfd, int *pfd);
 
 extern struct cr_img *open_image_at(int dfd, int type, unsigned long flags, ...);
 #define open_image(typ, flags, ...) open_image_at(-1, typ, flags, ##__VA_ARGS__)

criu/irmap.c

@@ -425,12 +425,10 @@ in:
 		close_image(*img);
 		if (dir == AT_FDCWD) {
 			pr_info("Searching irmap cache in parent\n");
-			dir = openat(get_service_fd(IMG_FD_OFF),
-					CR_PARENT_LINK, O_RDONLY);
+			if (open_parent(get_service_fd(IMG_FD_OFF), &dir))
+				return -1;
 			if (dir >= 0)
 				goto in;
-			if (errno != ENOENT)
-				return -1;
 		}
 
 		pr_info("No irmap cache\n");

criu/page-xfer.c

@@ -364,10 +364,8 @@ static int open_page_local_xfer(struct page_xfer *xfer, int fd_type, unsigned lo
 		return -1;
 
 	xfer->pi = open_pages_image(O_DUMP, xfer->pmi, &pages_id);
-	if (!xfer->pi) {
-		close_image(xfer->pmi);
-		return -1;
-	}
+	if (!xfer->pi)
+		goto err_pmi;
 
 	/*
 	 * Open page-read for parent images (if it exists). It will
@@ -386,14 +384,15 @@ static int open_page_local_xfer(struct page_xfer *xfer, int fd_type, unsigned lo
 		if (opts.stream)
 			goto out;
 
-		pfd = openat(get_service_fd(IMG_FD_OFF), CR_PARENT_LINK, O_RDONLY);
-		if (pfd < 0 && errno == ENOENT)
+		if (open_parent(get_service_fd(IMG_FD_OFF), &pfd))
+			goto err_pi;
+		if (pfd < 0)
 			goto out;
 
 		xfer->parent = xmalloc(sizeof(*xfer->parent));
 		if (!xfer->parent) {
 			close(pfd);
-			return -1;
+			goto err_pi;
 		}
 
 		ret = open_page_read_at(pfd, img_id, xfer->parent, pr_flags);
@@ -412,6 +411,12 @@ out:
 	xfer->write_pages = write_pages_loc;
 	xfer->close = close_page_xfer;
 	return 0;
+
+err_pi:
+	close_image(xfer->pi);
+err_pmi:
+	close_image(xfer->pmi);
+	return -1;
 }
 
 int open_page_xfer(struct page_xfer *xfer, int fd_type, unsigned long img_id)
@@ -936,8 +941,9 @@ int check_parent_local_xfer(int fd_type, unsigned long img_id)
 	if (opts.stream)
 		return 0;
 
-	pfd = openat(get_service_fd(IMG_FD_OFF), CR_PARENT_LINK, O_RDONLY);
-	if (pfd < 0 && errno == ENOENT)
+	if (open_parent(get_service_fd(IMG_FD_OFF), &pfd))
+		return -1;
+	if (pfd < 0)
 		return 0;
 
 	snprintf(path, sizeof(path), imgset_template[fd_type].fmt, img_id);

criu/pagemap.c

@@ -661,8 +661,9 @@ static int try_open_parent(int dfd, unsigned long id, struct page_read *pr, int
 	if (opts.stream)
 		goto out;
 
-	pfd = openat(dfd, CR_PARENT_LINK, O_RDONLY);
-	if (pfd < 0 && errno == ENOENT)
+	if (open_parent(dfd, &pfd))
+		goto err;
+	if (pfd < 0)
 		goto out;
 
 	parent = xmalloc(sizeof(*parent));
@@ -687,6 +688,7 @@ err_free:
 	xfree(parent);
 err_cl:
 	close(pfd);
+err:
 	return -1;
 }