util/nvmutil: r_type check in rw_gbe_file_part

i already send the right arg anyway. this is a
preventative bug fix against future maintenance.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -1456,7 +1456,11 @@ rw_gbe_file_part(size_t p, int rw_type,
 
 	uint8_t *mem_offset;
 
-	if (rw_type == IO_WRITE || rw_type == IO_PWRITE)
+	if (rw_type < IO_PREAD || rw_type > IO_PWRITE)
+		err(errno, "%s: %s: part %lu: invalid rw_type, %d",
+		    fname, rw_type_str, (unsigned long)p, rw_type);
+
+	if (rw_type == IO_PWRITE)
 		invert = 0;
 
 	/*
@@ -1564,9 +1568,11 @@ rw_file_exact(int fd, uint8_t *mem, size_t len,
 		return -1;
 	}
 
-	for (rc = 0, rv = 0; rc < len; rc += (size_t)rv) {
-		if ((rv = rw_file_once(fd, mem, len, off, rw_type, rc)) == -1)
+	for (rc = 0, rv = 0; rc < len; ) {
+		if ((rv = rw_file_once(fd, mem, len, off, rw_type, rc)) <= 0)
 			return -1;
+
+		rc += (size_t)rv;
 	}
 
 	return rc;
@@ -1615,9 +1621,6 @@ static ssize_t
 do_rw(int fd, uint8_t *mem,
     size_t len, off_t off, int rw_type)
 {
-	if ((unsigned int)rw_type > IO_PWRITE)
-		goto err_do_rw;
-
 	if (rw_type == IO_READ)
 		return read(fd, mem, len);
 
@@ -1627,7 +1630,6 @@ do_rw(int fd, uint8_t *mem,
 	if (rw_type == IO_PREAD || rw_type == IO_PWRITE)
 		return prw(fd, mem, len, off, rw_type);
 
-err_do_rw:
 	errno = EIO;
 	return -1;
 }
@@ -1648,8 +1650,11 @@ prw(int fd, void *mem, size_t nrw,
 	off_t off_orig;
 	ssize_t r;
 	int saved_errno;
+	int prw_type;
 
-	if ((unsigned int)(rw_type ^ IO_PREAD) > IO_WRITE) {
+	prw_type = rw_type ^ IO_PREAD;
+
+	if ((unsigned int)prw_type > IO_WRITE) {
 		errno = EIO;
 		return -1;
 	}
@@ -1660,7 +1665,7 @@ prw(int fd, void *mem, size_t nrw,
 		return -1;
 
 	do {
-		r = do_rw(fd, mem, nrw, off, rw_type ^ IO_PREAD);
+		r = do_rw(fd, mem, nrw, off, prw_type);
 	} while (r < 0 && errno == EINTR);
 
 	saved_errno = errno;