[PATCH v3 1/3] s390/debug: Fix NULL pointer dereference in debug_set_level()

[Mikhail Zaslonko <zaslonko@linux.ibm.com>]

Commit a2cec6863709 ("s390/debug: Add s390dbf kernel parameter")
incorrectly removed a null-id check from debug_set_level(), introducing
a possible NULL pointer dereference for debug-API users that put
debug_register() results unchecked into debug_set_level().

Fix this by moving the check from the internal _debug_set_level()
variant back to the external debug_set_level() wrapper.

Fixes: a2cec6863709 ("s390/debug: Add s390dbf kernel parameter")

Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
---
 arch/s390/kernel/debug.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index 14d2b58ad093..e06abf1dbc21 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -1074,9 +1074,6 @@ static void _debug_set_level(debug_info_t *id, int new_level)
 {
 	unsigned long flags;
 
-	if (!id)
-		return;
-
 	if (new_level == DEBUG_OFF_LEVEL) {
 		pr_info("%s: switched off\n", id->name);
 	} else if ((new_level > DEBUG_MAX_LEVEL) || (new_level < 0)) {
@@ -1101,6 +1098,9 @@ static void _debug_set_level(debug_info_t *id, int new_level)
  */
 void debug_set_level(debug_info_t *id, int new_level)
 {
+	if (!id)
+		return;
+
 	/* Level specified via kernel parameter takes precedence */
 	debug_get_param(id->name, &new_level, NULL);
 
-- 
2.55.0