Re: [PATCH v2] EDAC/thunderx: Fix some potential buffer overflow in thunderx_ocx_com_threaded_isr()

[Dan Carpenter]

On Sat, Oct 21, 2023 at 07:13:51PM +0200, Christophe JAILLET wrote:
> @@ -1127,27 +1128,26 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
>  				ARRAY_SIZE(ocx->com_err_ctx));
>  		ctx = &ocx->com_err_ctx[tail];
>  
> -		snprintf(msg, OCX_MESSAGE_SIZE, "%s: OCX_COM_INT: %016llx",
> -			ocx->edac_dev->ctl_name, ctx->reg_com_int);
> -
>  		decode_register(other, OCX_OTHER_SIZE,
>  				ocx_com_errors, ctx->reg_com_int);
>  
> -		strncat(msg, other, OCX_MESSAGE_SIZE);
> +		remaining = OCX_MESSAGE_SIZE;
> +		remaining -= scnprintf(msg, remaining, "%s: OCX_COM_INT: %016llx%s",
> +				       ocx->edac_dev->ctl_name, ctx->reg_com_int,
> +				       other);
>  
>  		for (lane = 0; lane < OCX_RX_LANES; lane++)
>  			if (ctx->reg_com_int & BIT(lane)) {
> -				snprintf(other, OCX_OTHER_SIZE,
> -					 "\n\tOCX_LNE_INT[%02d]: %016llx OCX_LNE_STAT11[%02d]: %016llx",
> -					 lane, ctx->reg_lane_int[lane],
> -					 lane, ctx->reg_lane_stat11[lane]);
> -
> -				strncat(msg, other, OCX_MESSAGE_SIZE);
> -
>  				decode_register(other, OCX_OTHER_SIZE,
>  						ocx_lane_errors,
>  						ctx->reg_lane_int[lane]);
> -				strncat(msg, other, OCX_MESSAGE_SIZE);
> +
> +				remaining -= scnprintf(msg + (OCX_MESSAGE_SIZE - remaining),
> +						       remaining,

Instead of doing "remaining -=" the canonincal way is "off +=".  Then
the snprintf() becomes:

	off += scnprintf(msg + off, OCX_MESSAGE_SIZE - off, ""\n\tOCX_...

Your way works but it makes my head hurt.

regards,
dan carpenter