mISDN: Fix memory leak in dsp_hwec_enable()

[ Upstream commit 0704a3d ]

dsp_hwec_enable() allocates dup pointer by kstrdup(arg),
but then it updates dup variable by strsep(&dup, ",").
As a result when it calls kfree(dup), the dup variable may be
a modified pointer that no longer points to the original allocated
memory, causing a memory leak.

The issue is the same pattern as fixed in commit c6a502c
("mISDN: Fix memory leak in dsp_pipeline_build()").

Fixes: 9a43816 ("mISDN: Remove VLAs")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250828081457.36061-1-linmq006@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Yuuoniy

drivers/isdn/mISDN/dsp_hwec.c

@@ -51,14 +51,14 @@ void dsp_hwec_enable(struct dsp *dsp, const char *arg)
 		goto _do;
 
 	{
-		char *dup, *tok, *name, *val;
+		char *dup, *next, *tok, *name, *val;
 		int tmp;
 
-		dup = kstrdup(arg, GFP_ATOMIC);
+		dup = next = kstrdup(arg, GFP_ATOMIC);
 		if (!dup)
 			return;
 
-		while ((tok = strsep(&dup, ","))) {
+		while ((tok = strsep(&next, ","))) {
 			if (!strlen(tok))
 				continue;
 			name = strsep(&tok, "=");