mISDN: Fix memory leak in dsp_pipeline_build()

dsp_pipeline_build() allocates dup pointer by kstrdup(cfg),
but then it updates dup variable by strsep(&dup, "|").
As a result when it calls kfree(dup), the dup variable contains NULL.

Found by Linux Driver Verification project (linuxtesting.org) with SVACE.
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: 960366cf ("Add mISDN DSP")
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/mISDN/dsp_pipeline.c

@@ -192,7 +192,7 @@ void dsp_pipeline_destroy(struct dsp_pipeline *pipeline)
 int dsp_pipeline_build(struct dsp_pipeline *pipeline, const char *cfg)
 {
 	int found = 0;
-	char *dup, *tok, *name, *args;
+	char *dup, *next, *tok, *name, *args;
 	struct dsp_element_entry *entry, *n;
 	struct dsp_pipeline_entry *pipeline_entry;
 	struct mISDN_dsp_element *elem;
@@ -203,10 +203,10 @@ int dsp_pipeline_build(struct dsp_pipeline *pipeline, const char *cfg)
 	if (!list_empty(&pipeline->list))
 		_dsp_pipeline_destroy(pipeline);
 
-	dup = kstrdup(cfg, GFP_ATOMIC);
+	dup = next = kstrdup(cfg, GFP_ATOMIC);
 	if (!dup)
 		return 0;
-	while ((tok = strsep(&dup, "|"))) {
+	while ((tok = strsep(&next, "|"))) {
 		if (!strlen(tok))
 			continue;
 		name = strsep(&tok, "(");