exit: Use READ_ONCE() for all oops/warn limit reads

Use a temporary variable to take full advantage of READ_ONCE() behavior.
Without this, the report (and even the test) might be out of sync with
the initial test.

Reported-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]
Fixes: 9fc9e27 ("panic: Introduce warn_limit")
Fixes: d4ccd54 ("exit: Put an upper limit on how often we can oops")
Cc: "Eric W. Biederman" <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Luis Chamberlain <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: tangmeng <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Tiezhu Yang <[email protected]>
Signed-off-by: Kees Cook <[email protected]>

Author: kees

kernel/exit.c

@@ -931,6 +931,7 @@ void __noreturn make_task_dead(int signr)
 	 * Then do everything else.
 	 */
 	struct task_struct *tsk = current;
+	unsigned int limit;
 
 	if (unlikely(in_interrupt()))
 		panic("Aiee, killing interrupt handler!");
@@ -954,8 +955,9 @@ void __noreturn make_task_dead(int signr)
 	 * To make sure this can't happen, place an upper bound on how often the
 	 * kernel may oops without panic().
 	 */
-	if (atomic_inc_return(&oops_count) >= READ_ONCE(oops_limit) && oops_limit)
-		panic("Oopsed too often (kernel.oops_limit is %d)", oops_limit);
+	limit = READ_ONCE(oops_limit);
+	if (atomic_inc_return(&oops_count) >= limit && limit)
+		panic("Oopsed too often (kernel.oops_limit is %d)", limit);
 
 	/*
 	 * We're taking recursive faults here in make_task_dead. Safest is to just

kernel/panic.c

@@ -231,12 +231,15 @@ static void panic_print_sys_info(bool console_flush)
 
 void check_panic_on_warn(const char *origin)
 {
+	unsigned int limit;
+
 	if (panic_on_warn)
 		panic("%s: panic_on_warn set ...\n", origin);
 
-	if (atomic_inc_return(&warn_count) >= READ_ONCE(warn_limit) && warn_limit)
+	limit = READ_ONCE(warn_limit);
+	if (atomic_inc_return(&warn_count) >= limit && limit)
 		panic("%s: system warned too often (kernel.warn_limit is %d)",
-		      origin, warn_limit);
+		      origin, limit);
 }
 
 /**