tmon: Check log file for common secuirty issues

The tmon logging system blindly opens its log file on a static path, making it very easy for someone to redirect that log information to inappropriate places or overwrite other users data. Do some easy checking to make sure we're not logging to a symlink or a file owned by another user. Signed-off-by: Neil Horman <[email protected]> Acked-by: Jacob Pan <[email protected]> Signed-off-by: Zhang Rui <[email protected]>
makiko-fly · Jul 1, 2014 · 951fda3 · 951fda3
1 parent 6b53326
commit 951fda3
Showing 1 changed file with 24 additions and 0 deletions.
diff --git a/tools/thermal/tmon/tmon.c b/tools/thermal/tmon/tmon.c
@@ -142,6 +142,7 @@ static void start_syslog(void)
 static void prepare_logging(void)
 {
 	int i;
+	struct stat logstat;
 
 	if (!logging)
 		return;
@@ -152,6 +153,29 @@ static void prepare_logging(void)
 		return;
 	}
 
+	if (lstat(TMON_LOG_FILE, &logstat) < 0) {
+		syslog(LOG_ERR, "Unable to stat log file %s\n", TMON_LOG_FILE);
+		fclose(tmon_log);
+		tmon_log = NULL;
+		return;
+	}
+
+	/* The log file must be a regular file owned by us */
+	if (S_ISLNK(logstat.st_mode)) {
+		syslog(LOG_ERR, "Log file is a symlink.  Will not log\n");
+		fclose(tmon_log);
+		tmon_log = NULL;
+		return;
+	}
+
+	if (logstat.st_uid != getuid()) {
+		syslog(LOG_ERR, "We don't own the log file.  Not logging\n");
+		fclose(tmon_log);
+		tmon_log = NULL;
+		return;
+	}
+
+
 	fprintf(tmon_log, "#----------- THERMAL SYSTEM CONFIG -------------\n");
 	for (i = 0; i < ptdata.nr_tz_sensor; i++) {
 		char binding_str[33]; /* size of long + 1 */