Re: [PATCH] net: wwan: iosm: Convert single instance struct member to flexible array

[Simon Horman <simon.horman@corigine.com>]

On Tue, Jun 20, 2023 at 12:42:38PM -0700, Kees Cook wrote:
> struct mux_adth actually ends with multiple struct mux_adth_dg members.
> This is seen both in the comments about the member:
> 
> /**
>  * struct mux_adth - Structure of the Aggregated Datagram Table Header.
>  ...
>  * @dg:		datagramm table with variable length
>  */
> 
> and in the preparation for populating it:
> 
>                         adth_dg_size = offsetof(struct mux_adth, dg) +
>                                         ul_adb->dg_count[i] * sizeof(*dg);
> 			...
>                         adth_dg_size -= offsetof(struct mux_adth, dg);
>                         memcpy(&adth->dg, ul_adb->dg[i], adth_dg_size);
> 
> This was reported as a run-time false positive warning:
> 
> memcpy: detected field-spanning write (size 16) of single field "&adth->dg" at drivers/net/wwan/iosm/iosm_ipc_mux_codec.c:852 (size 8)
> 
> Adjust the struct mux_adth definition and associated sizeof() math; no binary
> output differences are observed in the resulting object file.
> 
> Reported-by: Florian Klink <flokli@flokli.de>
> Closes: https://lore.kernel.org/lkml/dbfa25f5-64c8-5574-4f5d-0151ba95d232@gmail.com/
> Fixes: 1f52d7b62285 ("net: wwan: iosm: Enable M.2 7360 WWAN card support")
> Cc: M Chetan Kumar <m.chetan.kumar@intel.com>
> Cc: Bagas Sanjaya <bagasdotme@gmail.com>
> Cc: Intel Corporation <linuxwwan@intel.com>
> Cc: Loic Poulain <loic.poulain@linaro.org>
> Cc: Sergey Ryazanov <ryazanov.s.a@gmail.com>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/net/wwan/iosm/iosm_ipc_mux_codec.c | 15 ++++++---------
>  drivers/net/wwan/iosm/iosm_ipc_mux_codec.h |  2 +-
>  2 files changed, 7 insertions(+), 10 deletions(-)

Reviewed-by: Simon Horman <simon.horman@corigine.com>