trace: handle tracefs path truncation

If the tracefs mountpoint has a very long path we may exceed PATH_MAX. This is a system misconfiguration and the user must resolve it so that applications can perform path-based system calls successfully. This issue does not occur on real-world systems since tracefs is mounted on /sys/kernel/debug/tracing/, but the compiler is smart enough to foresee the possibility and warn about the unchecked snprintf(3) return value. This patch fixes the compiler warning. Reported-by: Markus Armbruster <[email protected]> Signed-off-by: Stefan Hajnoczi <[email protected]> Reviewed-by: Markus Armbruster <[email protected]> Reviewed-by: Liam Merwick <[email protected]> Message-id: [email protected] Message-Id: <[email protected]> Signed-off-by: Stefan Hajnoczi <[email protected]>
AndreRH · Mar 22, 2019 · fd98583 · fd98583
1 parent d97a39d
commit fd98583
Showing 1 changed file with 10 additions and 2 deletions.
diff --git a/trace/ftrace.c b/trace/ftrace.c
@@ -53,7 +53,11 @@ bool ftrace_init(void)
     }
 
     if (tracefs_found) {
-        snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir);
+        if (snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir)
+                >= sizeof(path)) {
+            fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
+            return false;
+        }
         trace_fd = open(path, O_WRONLY);
         if (trace_fd < 0) {
             if (errno == EACCES) {
@@ -72,7 +76,11 @@ bool ftrace_init(void)
             }
             close(trace_fd);
         }
-        snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir);
+        if (snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir)
+                >= sizeof(path)) {
+            fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
+            return false;
+        }
         trace_marker_fd = open(path, O_WRONLY);
         if (trace_marker_fd < 0) {
             perror("Could not open ftrace 'trace_marker' file");