Re: [PATCH][next] net: wwan: t7xx: Add __counted_by for struct t7xx_fsm_event and use struct_size()

[Kees Cook <keescook@chromium.org>]

On Mon, Oct 09, 2023 at 03:46:18PM -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
> 
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Looks right to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  drivers/net/wwan/t7xx/t7xx_state_monitor.c | 3 ++-
>  drivers/net/wwan/t7xx/t7xx_state_monitor.h | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wwan/t7xx/t7xx_state_monitor.c b/drivers/net/wwan/t7xx/t7xx_state_monitor.c
> index 80edb8e75a6a..0bc97430211b 100644
> --- a/drivers/net/wwan/t7xx/t7xx_state_monitor.c
> +++ b/drivers/net/wwan/t7xx/t7xx_state_monitor.c
> @@ -445,7 +445,8 @@ int t7xx_fsm_append_event(struct t7xx_fsm_ctl *ctl, enum t7xx_fsm_event_state ev
>  		return -EINVAL;
>  	}
>  
> -	event = kmalloc(sizeof(*event) + length, in_interrupt() ? GFP_ATOMIC : GFP_KERNEL);
> +	event = kmalloc(struct_size(event, data, length),
> +			in_interrupt() ? GFP_ATOMIC : GFP_KERNEL);
>  	if (!event)
>  		return -ENOMEM;
>  
> diff --git a/drivers/net/wwan/t7xx/t7xx_state_monitor.h b/drivers/net/wwan/t7xx/t7xx_state_monitor.h
> index b6e76f3903c8..b0b3662ae6d7 100644
> --- a/drivers/net/wwan/t7xx/t7xx_state_monitor.h
> +++ b/drivers/net/wwan/t7xx/t7xx_state_monitor.h
> @@ -102,7 +102,7 @@ struct t7xx_fsm_event {
>  	struct list_head	entry;
>  	enum t7xx_fsm_event_state event_id;
>  	unsigned int		length;
> -	unsigned char		data[];
> +	unsigned char		data[] __counted_by(length);
>  };
>  
>  struct t7xx_fsm_command {
> -- 
> 2.34.1
> 
> 

-- 
Kees Cook