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

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Message-ID: <YJovRPdOiaU6I+JK@mwanda>
Date:   Tue, 11 May 2021 10:16:20 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Mark Fasheh <mark@...heh.com>
Cc:     Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        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: [PATCH] ocfs2: fix snprintf() checking

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>
---
 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);
-- 
2.30.2