[PATCH 5.10 218/390] dyndbg: fix module.dyndbg handling

[Greg Kroah-Hartman]

From: Jim Cromie <jim.cromie@xxxxxxxxx>

[ Upstream commit 85d6b66d31c35158364058ee98fb69ab5bb6a6b1 ]

For CONFIG_DYNAMIC_DEBUG=N, the ddebug_dyndbg_module_param_cb()
stub-fn is too permissive:

bash-5.1# modprobe drm JUNKdyndbg
bash-5.1# modprobe drm dyndbgJUNK
[   42.933220] dyndbg param is supported only in CONFIG_DYNAMIC_DEBUG builds
[   42.937484] ACPI: bus type drm_connector registered

This caused no ill effects, because unknown parameters are either
ignored by default with an "unknown parameter" warning, or ignored
because dyndbg allows its no-effect use on non-dyndbg builds.

But since the code has an explicit feedback message, it should be
issued accurately.  Fix with strcmp for exact param-name match.

Fixes: b48420c1d301 dynamic_debug: make dynamic-debug work for module initialization
Reported-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Acked-by: Jason Baron <jbaron@xxxxxxxxxx>
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
Link: https://lore.kernel.org/r/20220904214134.408619-3-jim.cromie@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/dynamic_debug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index a57ee75342cf..b0b23679b2c2 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -196,7 +196,7 @@ static inline int ddebug_remove_module(const char *mod)
 static inline int ddebug_dyndbg_module_param_cb(char *param, char *val,
 						const char *modname)
 {
-	if (strstr(param, "dyndbg")) {
+	if (!strcmp(param, "dyndbg")) {
 		/* avoid pr_warn(), which wants pr_fmt() fully defined */
 		printk(KERN_WARNING "dyndbg param is supported only in "
 			"CONFIG_DYNAMIC_DEBUG builds\n");
-- 
2.35.1