linux-kernel - Re: [PATCH] ima: fix off-by-one comparison on template name length

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Date:   Wed, 21 Sep 2016 15:10:11 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Colin King <colin.king@...onical.com>
Cc:     James Morris <james.l.morris@...cle.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-ima-devel@...ts.sourceforge.net,
        linux-ima-user@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ima: fix off-by-one comparison on template name length

Hi Colin,

On Tue, 2016-09-20 at 18:25 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The comparison of dr_v1->template_name_len is off-by-one, so
> currently if the length is MAX_TEMPLATE_NAME_LEN we end up
> with an out-of-bounds write on template_name when the terminating
> zero character is written. Fix the comparison.
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Thank you for the bug report.  The patch that introduces this bug is in
the -mm tree.  The next posting will include this bug fix.

Thanks!

Mimi

> ---
>  security/integrity/ima/ima_template.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
> index 24775f3..004723c 100644
> --- a/security/integrity/ima/ima_template.c
> +++ b/security/integrity/ima/ima_template.c
> @@ -395,7 +395,7 @@ int ima_restore_measurement_list(loff_t size, void *buf)
>  			hdr_v1->template_name_len =
>  			    le32_to_cpu(hdr_v1->template_name_len);
> 
> -		if ((hdr_v1->template_name_len > MAX_TEMPLATE_NAME_LEN) ||
> +		if ((hdr_v1->template_name_len >= MAX_TEMPLATE_NAME_LEN) ||
>  		    ((bufp + hdr_v1->template_name_len) > bufendp)) {
>  			pr_err("attempting to restore a template name \
>  				that is too long\n");