linux-kernel - Re: [PATCH] ocfs2: fix snprintf() checking

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Date:   Tue, 11 May 2021 20:54:53 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Mark Fasheh <mark@...heh.com>
Cc:     Joel Becker <jlbec@...lplan.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Gang He <ghe@...e.com>, ocfs2-devel@....oracle.com,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ocfs2: fix snprintf() checking



On 5/11/21 3:16 PM, Dan Carpenter wrote:
> The snprintf() function returns the number of bytes which would have
> been printed if the buffer was large enough.  In other words it can
> return ">= remain" but this code assumes it returns "== remain".
> 
> The run time impact of this bug is not very severe.  The next iteration
> through the loop would trigger a WARN() when we pass a negative limit
> to snprintf().  We would then return success instead of -E2BIG.
> 
> The kernel implementation of snprintf() will never return negatives so
> there is no need to check and I have deleted that dead code.
> 
> Fixes: a860f6eb4c6a ("ocfs2: sysfile interfaces for online file check")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

Looks good. But the last 2 sections are introduced by:
74ae4e104dfc ocfs2: Create stack glue sysfs files.

With 'Fixes' tag updated,
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>

> ---
>  fs/ocfs2/filecheck.c | 6 +-----
>  fs/ocfs2/stackglue.c | 8 ++------
>  2 files changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ocfs2/filecheck.c b/fs/ocfs2/filecheck.c
> index 90b8d300c1ee..de56e6231af8 100644
> --- a/fs/ocfs2/filecheck.c
> +++ b/fs/ocfs2/filecheck.c
> @@ -326,11 +326,7 @@ static ssize_t ocfs2_filecheck_attr_show(struct kobject *kobj,
>  		ret = snprintf(buf + total, remain, "%lu\t\t%u\t%s\n",
>  			       p->fe_ino, p->fe_done,
>  			       ocfs2_filecheck_error(p->fe_status));
> -		if (ret < 0) {
> -			total = ret;
> -			break;
> -		}
> -		if (ret == remain) {
> +		if (ret >= remain) {
>  			/* snprintf() didn't fit */
>  			total = -E2BIG;
>  			break;
> diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
> index d50e8b8dfea4..16f1bfc407f2 100644
> --- a/fs/ocfs2/stackglue.c
> +++ b/fs/ocfs2/stackglue.c
> @@ -500,11 +500,7 @@ static ssize_t ocfs2_loaded_cluster_plugins_show(struct kobject *kobj,
>  	list_for_each_entry(p, &ocfs2_stack_list, sp_list) {
>  		ret = snprintf(buf, remain, "%s\n",
>  			       p->sp_name);
> -		if (ret < 0) {
> -			total = ret;
> -			break;
> -		}
> -		if (ret == remain) {
> +		if (ret >= remain) {
>  			/* snprintf() didn't fit */
>  			total = -E2BIG;
>  			break;
> @@ -531,7 +527,7 @@ static ssize_t ocfs2_active_cluster_plugin_show(struct kobject *kobj,
>  	if (active_stack) {
>  		ret = snprintf(buf, PAGE_SIZE, "%s\n",
>  			       active_stack->sp_name);
> -		if (ret == PAGE_SIZE)
> +		if (ret >= PAGE_SIZE)
>  			ret = -E2BIG;
>  	}
>  	spin_unlock(&ocfs2_stack_lock);
>