df plugin: Guard strcmp() against being passed NULL pointers.

Issue: #1835

diff --git a/src/df.c b/src/df.c
index 4a86799..af54c92 100644 (file)
--- a/src/df.c
+++ b/src/df.c
@@ -229,7 +229,10 @@ static int df_read (void)
                        }
 
                        /* Duplicate found: leave non-NULL dup_ptr. */
-                       if (by_device && (strcmp (mnt_ptr->spec_device, dup_ptr->spec_device) == 0))
+                       if (by_device
+                            && (mnt_ptr->spec_device != NULL)
+                            && (dup_ptr->spec_device != NULL)
+                            && (strcmp (mnt_ptr->spec_device, dup_ptr->spec_device) == 0))
                                break;
                        else if (!by_device && (strcmp (mnt_ptr->dir, dup_ptr->dir) == 0))
                                break;