[tip:core/core] overflow.h: Add comment documenting __ab_c_size()

[tip-bot for Rasmus Villemoes <tipbot@zytor.com>]

Commit-ID:  e0478542cfd4d993e38d5f92a3f3ecd238805e96
Gitweb:     https://git.kernel.org/tip/e0478542cfd4d993e38d5f92a3f3ecd238805e96
Author:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
AuthorDate: Wed, 10 Apr 2019 22:27:25 +0200
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Fri, 12 Apr 2019 13:44:24 +0200

overflow.h: Add comment documenting __ab_c_size()

__ab_c_size() is a somewhat opaque name. Document its purpose, and while
at it, rename the parameters to actually match the abc naming.

 [ bp: glued a complete patch from chunks on LKML. ]

Reported-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Link: https://lkml.kernel.org/r/20190405045711.30339-1-bp@alien8.de
---
 include/linux/overflow.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

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;