linux-kernel - Re: [PATCH] i2c: mux: harden i2c_mux

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Message-ID: <202209160101.2A240E9@keescook>
Date:   Fri, 16 Sep 2022 01:07:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Peter Rosin <peda@...ntia.se>, Wolfram Sang <wsa@...nel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] i2c: mux: harden i2c_mux_alloc() against integer
 overflows

On Thu, Sep 15, 2022 at 05:09:45PM +0300, Dan Carpenter wrote:
> It would probaby be useful to mark passed data as explicitly unsafe for
> integer overflows.  Smatch already tracks user data.  And if the user
> data has been capped to an unknown value.  But this would be a
> completely separate flag which says that "this value came from
> size_add/mul()".

I really want a __must_check_type(size_t) attribute or something for
functions, so we can get a subset of -Wconversion warnings, etc.

> drivers/char/tpm/eventlog/tpm2.c:57 tpm2_bios_measurements_start() warn: using integer overflow function 'size_add()' for math
> [...]
> drivers/net/ethernet/intel/ice/ice_flex_pipe.c:2070 ice_pkg_buf_reserve_section() warn: using integer overflow function 'size_mul()' for math

I see size_add() and size_mul() here. I would have expected some
size_sub() opportunities too? Did nothing pop out?

-- 
Kees Cook