linux-kernel - Re: [PATCH v2] EDAC/thunderx: Fix some potential buffer overflow in thunderx_ocx_com_threaded

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Message-ID: <70bd7480-508a-451d-bc0a-f78e652cf511@kadam.mountain>
Date:   Tue, 24 Oct 2023 08:35:33 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     keescook@...omium.org, Robert Richter <rric@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sergey Temerkhanov <s.temerkhanov@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        linux-edac@...r.kernel.org
Subject: Re: [PATCH v2] EDAC/thunderx: Fix some potential buffer overflow in
 thunderx_ocx_com_threaded_isr()

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