cbfstool: accept read-only files when possible

cbfstool tries opening the input file for write access even if the
command does not require modifying the file.

Let's not request write access unless it is necessary, this way one
can examine write protected files without sudo.

BRANCH=none
BUG=none
TEST=running

   cbfstool /build/<board>/firmware/image.bin print

   in chroot does not require root access any more.

Change-Id: Ic4e4cc389b160da190e44a676808f5c4e6625567
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: ef6a8e25d9e257d7de4cc6b94e510234fe20a56d
Original-Change-Id: I871f32f0662221ffbdb13bf0482cb285ec184d07
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/317300
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/12931
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

util/cbfstool/cbfstool.c

@@ -38,7 +38,10 @@ struct command {
 	int (*function) (void);
 	// Whether to populate param.image_region before invoking function
 	bool accesses_region;
-	// Whether to write that region's contents back to image_file at the end
+	// This set to true means two things:
+	// - in case of a command operating on a region, the region's contents
+	//   will be written back to image_file at the end
+	// - write access to the file is required
 	bool modifies_region;
 };
 
@@ -1014,7 +1017,7 @@ static const struct command commands[] = {
 	{"print", "H:r:vh?", cbfs_print, true, false},
 	{"read", "r:f:vh?", cbfs_read, true, false},
 	{"remove", "H:r:n:vh?", cbfs_remove, true, true},
-	{"update-fit", "H:r:n:x:vh?", cbfs_update_fit, true, false},
+	{"update-fit", "H:r:n:x:vh?", cbfs_update_fit, true, true},
 	{"write", "r:f:udvh?", cbfs_write, true, true},
 };
 
@@ -1372,8 +1375,11 @@ int main(int argc, char **argv)
 				return 1;
 			}
 		} else {
+			bool write_access = commands[i].modifies_region;
+
 			param.image_file =
-				partitioned_file_reopen(image_name);
+				partitioned_file_reopen(image_name,
+							write_access);
 		}
 		if (!param.image_file)
 			return 1;
@@ -1429,7 +1435,6 @@ int main(int argc, char **argv)
 
 		if (commands[i].modifies_region) {
 			assert(param.image_file);
-			assert(commands[i].accesses_region);
 			for (unsigned region = 0; region < num_regions;
 								++region) {
 

util/cbfstool/partitioned_file.c

@@ -49,11 +49,13 @@ static unsigned count_selected_fmap_entries(const struct fmap *fmap,
 	return count;
 }
 
-static partitioned_file_t *reopen_flat_file(const char *filename)
+static partitioned_file_t *reopen_flat_file(const char *filename,
+					    bool write_access)
 {
 	assert(filename);
-
 	struct partitioned_file *file = calloc(1, sizeof(*file));
+	const char *access_mode;
+
 	if (!file) {
 		ERROR("Failed to allocate partitioned file structure\n");
 		return NULL;
@@ -64,7 +66,9 @@ static partitioned_file_t *reopen_flat_file(const char *filename)
 		return NULL;
 	}
 
-	file->stream = fopen(filename, "rb+");
+	access_mode = write_access ?  "rb+" : "rb";
+	file->stream = fopen(filename, access_mode);
+
 	if (!file->stream) {
 		perror(filename);
 		partitioned_file_close(file);
@@ -161,11 +165,12 @@ partitioned_file_t *partitioned_file_create(const char *filename,
 	return file;
 }
 
-partitioned_file_t *partitioned_file_reopen(const char *filename)
+partitioned_file_t *partitioned_file_reopen(const char *filename,
+					    bool write_access)
 {
 	assert(filename);
 
-	partitioned_file_t *file = reopen_flat_file(filename);
+	partitioned_file_t *file = reopen_flat_file(filename, write_access);
 	if (!file)
 		return NULL;
 

util/cbfstool/partitioned_file.h

@@ -71,9 +71,11 @@ partitioned_file_t *partitioned_file_create(const char *filename,
  * caller, and must later be passed to partitioned_file_close();
  *
  * @param filename      Name of the file to read in
+ * @param write_access  True if the file needs to be modified
  * @return              Caller-owned partitioned file, or NULL on error
  */
-partitioned_file_t *partitioned_file_reopen(const char *filename);
+partitioned_file_t *partitioned_file_reopen(const char *filename,
+					    bool write_access);
 
 /**
  * Write a buffer's contents to its original region within a segmented file.