[PATCH 4.19 v2 15/15] exit: Use READ_ONCE() for all oops/warn limit reads

Eric Biggers
2023-02-03T00:29:03Z

From: Kees Cook <keescook@chromium.org>

commit 7535b832c6399b5ebfc5b53af5c51dd915ee2538 upstream.

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 <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/Y5x7GXeluFmZ8E0E@hirez.programming.kicks-ass.net
Fixes: 9fc9e278a5c0 ("panic: Introduce warn_limit")
Fixes: d4ccd54d28d3 ("exit: Put an upper limit on how often we can oops")
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Jann Horn <jannh@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: tangmeng <tangmeng@uniontech.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
kernel/exit.c | 6 ++++--
kernel/panic.c | 7 +++++--
2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index b2f0aaf6bee78..02360ec3b1225 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -975,6 +975,7 @@ void __noreturn make_task_dead(int signr)
* Take the task off the cpu after something catastrophic has
* happened.
*/
+ unsigned int limit;

/*
* Every time the system oopses, if the oops happens while a reference
@@ -986,8 +987,9 @@ 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);

do_exit(signr);
}
diff --git a/kernel/panic.c b/kernel/panic.c
index dbb6e27d33e10..982ecba286c08 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -168,12 +168,15 @@ EXPORT_SYMBOL(nmi_panic);

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);
}

/**
--
2.39.1