ipl_tools/cmd_lsreipl.c: Construct sysfs paths with util_path_sysfs()

The default sysfs path is always set to '/sys' unless the SYSFS_ROOT
environment variable is defined.

To address security concerns, secure_getenv() is used within
util_path_sysfs() to protect against malicious values in SYSFS_ROOT.
Additionally, constructing the sysfs path dynamically in an allocated
buffer, rather than using a fixed-size buffer, helps prevent potential
buffer overflows.

These modifications also significantly improve testability by allowing
sysfs read operations to be redirected to an alternative file path,
which enables testing without affecting the active system state.

Signed-off-by: Jan Polensky <japo@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

ipl_tools/system.c

@@ -9,7 +9,7 @@
  * it under the terms of the MIT license. See LICENSE for details.
  */
 
-#include "lib/util_libc.h"
+#include "lib/util_path.h"
 #include "ipl_tools.h"
 
 /*
@@ -84,7 +84,7 @@ void read_fw_str(char *string, const char *file, size_t len)
 {
 	char *path;
 
-	util_asprintf(&path, "/sys/firmware/%s", file);
+	path = util_path_sysfs("firmware/%s", file);
 	read_str(string, path, len);
 	free(path);
 }