linux-kernel - Re: [PATCH v2] panic: prevent panic

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Message-ID: <20200714025058.GZ12769@casper.infradead.org>
Date:   Tue, 14 Jul 2020 03:50:58 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Changming <charley.ashbringer@...il.com>, rdunlap@...radead.org,
        keescook@...omium.org, mcgrof@...nel.org, yzaikin@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] panic: prevent panic_timeout * 1000 from overflow

On Mon, Jul 13, 2020 at 06:57:39PM -0700, Andrew Morton wrote:
> +++ a/kernel/panic.c
> @@ -313,13 +313,16 @@ void panic(const char *fmt, ...)
>  		 * Delay timeout seconds before rebooting the machine.
>  		 * We can't use the "normal" timers since we just panicked.
>  		 */
> +		u64 timeout = panic_timeout * 1000;	/* avoid overflow */

1000ULL to not truncate before the assignment.

> +		u64 timer;

... as you implied later

		u64 timer, timer_next;

> (untested)

Well, there's the rub.  Testing requires 49 days (2^32 / 1000 seconds).