[PATCH v5 3/4] panic: fix va_list reuse in panic_try_force_cpu()

[Bradley Morgan <include@grrlz.net>]

vsnprintf() consumes the caller's va_list. When the redirect fails,
vpanic() reuses it for the panic message, which is undefined
behavior. Use va_copy().

Fixes: 2e171ab29f91 ("panic: add panic_force_cpu= parameter to redirect panic to a specific CPU")
Cc: stable@vger.kernel.org
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
 kernel/panic.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 74065c860779..a483587fdd2f 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -416,7 +416,12 @@ static bool panic_try_force_cpu(const char *fmt, va_list args)
 	 * fall back to static message for early boot panics or allocation failure.
 	 */
 	if (panic_force_buf) {
-		vsnprintf(panic_force_buf, PANIC_MSG_BUFSZ, fmt, args);
+		va_list ap;
+
+		/* Do not consume args, the caller reuses it if we fail */
+		va_copy(ap, args);
+		vsnprintf(panic_force_buf, PANIC_MSG_BUFSZ, fmt, ap);
+		va_end(ap);
 		msg = panic_force_buf;
 	} else {
 		msg = "Redirected panic (buffer unavailable)";
-- 
2.47.3