modprobe: protect against possible SEGV

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/modutils/modprobe.c b/modutils/modprobe.c
index 2860ae05d..f339fbdbe 100644
--- a/modutils/modprobe.c
+++ b/modutils/modprobe.c
@@ -80,12 +80,14 @@ static int read_config(const char *path);
 static char *gather_options_str(char *opts, const char *append)
 {
         /* Speed-optimized. We call gather_options_str many times. */
-        if (opts == NULL) {
-                opts = xstrdup(append);
-        } else {
-                int optlen = strlen(opts);
-                opts = xrealloc(opts, optlen + strlen(append) + 2);
-                sprintf(opts + optlen, " %s", append);
+        if (append) {
+                if (opts == NULL) {
+                        opts = xstrdup(append);
+                } else {
+                        int optlen = strlen(opts);
+                        opts = xrealloc(opts, optlen + strlen(append) + 2);
+                        sprintf(opts + optlen, " %s", append);
+                }
         }
         return opts;
 }