[PATCH v3] docs: deprecated.rst: Clarify open-coded arithmetic with literals

From: Len Baker
Date: Sat Sep 25 2021 - 10:35:38 EST

Although using literals for size calculation in allocator arguments may
be harmless due to compiler warnings in case of overflows, it is better
to refactor the code to avoid the use of open-coded arithmetic.

So, clarify the preferred way in these cases.

Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Len Baker <len.baker@xxxxxxx>
Changelog v1 -> v2
- Clarify the sentence by changing "keep <foo> out" with "avoid <foo>"
(Joe Perches).

Changelog v2 -> v3
- Reword the sentence to comunicate better (Jonathan Corbet).

The previous version can be found here [1].

[1] https://lore.kernel.org/linux-hardening/20210829144716.2931-1-len.baker@xxxxxxx/

Documentation/process/deprecated.rst | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index 8ced754a5a0f..388cb19f5dbb 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -59,8 +59,9 @@ risk of them overflowing. This could lead to values wrapping around and a
smaller allocation being made than the caller was expecting. Using those
allocations could lead to linear overflows of heap memory and other
misbehaviors. (One exception to this is literal values where the compiler
-can warn if they might overflow. Though using literals for arguments as
-suggested below is also harmless.)
+can warn if they might overflow. However, the preferred way in these
+cases is to refactor the code as suggested below to avoid the open-coded

For example, do not use ``count * size`` as an argument, as in::