linux-kernel - Re: [PATCH] overflow.h: Rename __ab_c_size() to __calc

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Message-ID: <3fefb03d-3ea0-5a08-f00c-09a47b17f2a8@rasmusvillemoes.dk>
Date:   Fri, 5 Apr 2019 10:09:31 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Borislav Petkov <bp@...en8.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] overflow.h: Rename __ab_c_size() to __calc_size()

On 05/04/2019 09.52, Borislav Petkov wrote:
> On Fri, Apr 05, 2019 at 08:26:45AM +0200, Rasmus Villemoes wrote:

>> It computes a*b+c with overflow checking at each step. calc_size
>> is way too generic and doesn't say anything at all about how the
>> calc(ulation) is done.
> 
> Ok, whatever.
> 
> Then it would need at least a comment above it to state what it does. I
> don't want to go and parse the macros each time.

It's an internal helper, and struct_size is fully kernel-doc'ed. But
yeah, a comment wouldn't hurt, and let's rename the parameters so they
match the abc naming.

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 40b48e2133cb..6534a727cadb 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -278,11 +278,15 @@ static inline __must_check size_t
array3_size(size_t a, size_t b, size_t c)
        return bytes;
 }

-static inline __must_check size_t __ab_c_size(size_t n, size_t size,
size_t c)
+/*
+ * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
+ * struct_size() below.
+ */
+static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
 {
        size_t bytes;

-       if (check_mul_overflow(n, size, &bytes))
+       if (check_mul_overflow(a, b, &bytes))
                return SIZE_MAX;
        if (check_add_overflow(bytes, c, &bytes))
                return SIZE_MAX;


Rasmus