From: Kees Cook <keescook@chromium.org>
To: David Laight <David.Laight@aculab.com>
Cc: "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
'Andy Shevchenko' <andriy.shevchenko@linux.intel.com>,
'Andrew Morton' <akpm@linux-foundation.org>,
"'Matthew Wilcox (Oracle)'" <willy@infradead.org>,
'Christoph Hellwig' <hch@infradead.org>,
"'Jason A. Donenfeld'" <Jason@zx2c4.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH next v3 0/5] minmax: Relax type checks in min() and max().
Date: Mon, 14 Aug 2023 14:21:02 -0700 [thread overview]
Message-ID: <202308141416.89AC5C2@keescook> (raw)
In-Reply-To: <01e3e09005e9434b8f558a893a47c053@AcuMS.aculab.com>
On Fri, Aug 04, 2023 at 10:50:59AM +0000, David Laight wrote:
> [...]
> I also suspect that many of the min_t(u16, ...) are actually wrong.
> For example copy_data() in printk_ringbuffer.c contains:
> data_size = min_t(u16, buf_size, len);
> Here buf_size is 'unsigned int' and len 'u16', pass a 64k buffer
> (can you prove that doesn't happen?) and no data is returned.
Stars aligning... this exact bug (as you saw in the other thread[1]) got
hit. And in the analysis, I came to the same conclusion: min_t() is a
serious foot-gun, and we should be able to make min() Just Work in the
most common situations.
It seems like the existing type_max/type_min macros could be used to
figure out that the args are safe to appropriately automatically cast,
etc. e.g. type_max(u16) <= type_max(unsigned int) && type_min(u16) >=
type_min(unsigned int) ...
-Kees
[1] https://lore.kernel.org/all/20230811054528.never.165-kees@kernel.org/
--
Kees Cook
next prev parent reply other threads:[~2023-08-14 21:22 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-04 10:50 [PATCH next v3 0/5] minmax: Relax type checks in min() and max() David Laight
2023-08-04 10:53 ` [PATCH v3 1/5] minmax: Add min_unsigned(a, b) and max_unsigned(a, b) David Laight
2023-08-04 10:54 ` [PATCH v3 2/5] minmax: Allow min()/max()/clamp() if the arguments have the same signedness David Laight
2023-08-04 10:55 ` [PATCH v3 3/5] minmax: Fix indentation of __cmp_once() and __clamp_once() David Laight
2023-08-04 10:55 ` [PATCH v3 4/5] minmax: Allow comparisons of 'int' against 'unsigned char/short' David Laight
2023-08-04 10:56 ` [PATCH v3 5/5] minmax: Relax check to allow comparison between int and small unsigned constants David Laight
2023-08-04 18:14 ` Linus Torvalds
2023-08-07 10:50 ` David Laight
2023-08-07 15:48 ` Linus Torvalds
2023-08-10 8:29 ` David Laight
2023-08-10 19:46 ` Linus Torvalds
2023-08-14 8:04 ` David Laight
2023-08-14 14:51 ` David Laight
2023-08-14 15:29 ` David Laight
2023-08-14 21:21 ` Kees Cook [this message]
2023-08-15 8:55 ` [PATCH next v3 0/5] minmax: Relax type checks in min() and max() David Laight
2023-08-21 18:24 ` Kees Cook
2023-08-22 17:35 ` Linus Torvalds
2023-08-23 8:42 ` David Laight
2023-08-23 8:52 ` David Laight
2023-08-23 15:32 ` Linus Torvalds
2023-08-24 9:05 ` David Laight
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