Create debug log file with more sane file permissions

Previously the file permissions for the debug log file were not
explicitly set. Instead it was implicitly relying on a secure umask,
which in most cases would result in a file that is world-readable. This
is a violation of good practices, since not every user should have
access to sensitive information that might be contained in the debug log
file.

Explicitly set sane default file permissions in case the file is newly
created.

Unfortunately the fopen(3) function does not provide such a facility, so
the approach needs to be changed in the following way:

1) The file descriptor needs to be created manually using the open(3)
function with the correct flags and the desired mode set.

2) fdopen(3) can then be used on the file descriptor to associate a file
stream with it.

Note: This modification will not change the file permissions of any
already existing debug log files, and only applies to newly created
ones.

Signed-off-by: Karol Babioch <karol@babioch.de>

src/utils/wpa_debug.c

@@ -58,6 +58,10 @@ static int wpa_to_android_level(int level)
 #ifndef CONFIG_NO_STDOUT_DEBUG
 
 #ifdef CONFIG_DEBUG_FILE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
 static FILE *out_file = NULL;
 #endif /* CONFIG_DEBUG_FILE */
 
@@ -539,6 +543,8 @@ int wpa_debug_reopen_file(void)
 int wpa_debug_open_file(const char *path)
 {
 #ifdef CONFIG_DEBUG_FILE
+	int out_fd;
+
 	if (!path)
 		return 0;
 
@@ -548,10 +554,20 @@ int wpa_debug_open_file(const char *path)
 		last_path = os_strdup(path);
 	}
 
-	out_file = fopen(path, "a");
+	out_fd = open(path, O_CREAT | O_APPEND | O_WRONLY,
+		      S_IRUSR | S_IWUSR | S_IRGRP);
+	if (out_fd < 0) {
+		wpa_printf(MSG_ERROR,
+			   "%s: Failed to open output file descriptor, using standard output",
+			   __func__);
+		return -1;
+	}
+
+	out_file = fdopen(out_fd, "a");
 	if (out_file == NULL) {
 		wpa_printf(MSG_ERROR, "wpa_debug_open_file: Failed to open "
 			   "output file, using standard output");
+		close(out_fd);
 		return -1;
 	}
 #ifndef _WIN32