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Message-ID: <42a1e2099fe141c3a57e808cbf06d8a0@AcuMS.aculab.com>
Date: Mon, 14 Aug 2023 10:42:26 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Kees Cook' <keescook@...omium.org>, Petr Mladek <pmladek@...e.com>
CC: Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
John Ogness <john.ogness@...utronix.de>,
"Vijay Balakrishna" <vijayb@...ux.microsoft.com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
Tony Luck <tony.luck@...el.com>,
"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: RE: [PATCH] printk: ringbuffer: Fix truncating buffer size min_t cast
From: Kees Cook
> Sent: 11 August 2023 06:46
>
> If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
> copy_data() was causing writes to truncate. This manifested as output
> bytes being skipped, seen as %NUL bytes in pstore dumps when the available
> record size was larger than 65536. Fix the cast to no longer truncate
> the calculation.
>
...
> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> index 2dc4d5a1f1ff..fde338606ce8 100644
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> @@ -1735,7 +1735,7 @@ static bool copy_data(struct prb_data_ring *data_ring,
> if (!buf || !buf_size)
> return true;
>
> - data_size = min_t(u16, buf_size, len);
> + data_size = min_t(unsigned int, buf_size, len);
I'd noticed that during one of my test compiles while looking
at making min() less fussy.
A better fix would be:
data_size = min(buf_size + 0u, len);
Or put an ack on my patch 3/5 to minmax.h and then min(buf_size, len)
will be fine (because both arguments are unsigned).
David
>
> memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */
> return true;
> --
> 2.34.1
-
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