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

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  [PATCH] ima: fix off-by-one comparison on template name length Colin King <colin.king@canonical.com> - 2016-09-20 19:30 +0200
    Re: [PATCH] ima: fix off-by-one comparison on template name length Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-09-21 21:20 +0200

#1487537 — [PATCH] ima: fix off-by-one comparison on template name length

From: Colin Ian King <colin.king@canonical.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@canonical.com>
---
 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");
-- 
2.9.3

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#1488337

Hi Colin,

On Tue, 2016-09-20 at 18:25 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.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@canonical.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");

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