fdt: Check return value of fdt_get_name() calls

fdt_get_name() can return NULL and set len to a negative error code.
fdt_find_regions() does not check for this, leading to a potential NULL
pointer dereference and a buffer out-of-bounds write during signature
verification of an untrusted FIT. fdt_next_region(), fdt_check_full(),
and display_fdt_by_regions() also lack validation.

Add NULL checks and propagate the error code from fdt_get_name()
to the caller.

Signed-off-by: Anton Ivanov <anton@binarly.io>
Reviewed-by: Simon Glass <sjg@chromium.org>

boot/fdt_region.c

@@ -88,6 +88,8 @@ int fdt_find_regions(const void *fdt, char * const inc[], int inc_count,
 			if (depth == FDT_MAX_DEPTH)
 				return -FDT_ERR_BADSTRUCTURE;
 			name = fdt_get_name(fdt, offset, &len);
+			if (!name)
+				return len;
 
 			/* The root node must have an empty name */
 			if (!depth && *name)
@@ -563,6 +565,9 @@ int fdt_next_region(const void *fdt,
 			if (p.depth == FDT_MAX_DEPTH)
 				return -FDT_ERR_BADSTRUCTURE;
 			name = fdt_get_name(fdt, offset, &len);
+			if (!name)
+				return len;
+
 			if (p.end - path + 2 + len >= path_len)
 				return -FDT_ERR_NOSPACE;
 

scripts/dtc/libfdt/fdt_ro.c

@@ -940,6 +940,9 @@ int fdt_check_full(const void *fdt, size_t bufsize)
 				int len;
 
 				name = fdt_get_name(fdt, offset, &len);
+				if (!name)
+					return len;
+
 				if (*name || len)
 					return -FDT_ERR_BADLAYOUT;
 			}

tools/fdtgrep.c

@@ -355,6 +355,9 @@ static int display_fdt_by_regions(struct display_info *disp, const void *blob,
 
 		case FDT_BEGIN_NODE:
 			name = fdt_get_name(blob, offset, &len);
+			if (!name)
+				return len;
+
 			fprintf(f, "%*s%s {", depth++ * shift, "",
 				*name ? name : "/");
 			break;