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exit: Use READ_ONCE() for all oops/warn limit reads
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commit 7535b83 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: 9fc9e27 ("panic: Introduce warn_limit")
Fixes: d4ccd54 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Kees Cook authored and Greg Kroah-Hartman committed Feb 6, 2023
1 parent 6fff4e2 commit 4ba2f65
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Showing 2 changed files with 9 additions and 4 deletions.
6 changes: 4 additions & 2 deletions kernel/exit.c
Original file line number Diff line number Diff line change
Expand Up @@ -973,6 +973,7 @@ 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
Expand All @@ -984,8 +985,9 @@ 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);
}
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7 changes: 5 additions & 2 deletions kernel/panic.c
Original file line number Diff line number Diff line change
Expand Up @@ -165,12 +165,15 @@ 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);
}

/**
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