linux-kernel - [PATCH 5/7] Handle snprintf calulation more graceful in v9fs

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Message-ID: <fc83a0af-1e80-9388-27ef-329a6483e053@x41-dsec.de>
Date:   Wed, 11 Oct 2017 10:28:37 +0200
From:   Eric Sesterhenn <eric.sesterhenn@...-dsec.de>
To:     linux-kernel@...r.kernel.org
Subject: [PATCH 5/7] Handle snprintf calulation more graceful in v9fs


snprintf might return a value bigger than limit when the string gets
truncated, which would cause the return value to become bogus.

Signed-off-by: Eric Sesterhenn <eric.sesterhenn@...-dsec.>
---
 fs/9p/v9fs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 8fb89ddc6cc7..9e7cefc26ad9 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -552,6 +552,10 @@ static ssize_t caches_show(struct kobject *kobj,
 	list_for_each_entry(v9ses, &v9fs_sessionlist, slist) {
 		if (v9ses->cachetag) {
 			n = snprintf(buf, limit, "%s\n", v9ses->cachetag);
+			if (n > limit) {
+				count = PAGE_SIZE;
+				break;
+			}
 			if (n < 0) {
 				count = n;
 				break;

-- 
Eric Sesterhenn (Principal Security Consultant)
X41 D-SEC GmbH, Dennewartstr. 25-27, D-52068 Aachen
T: +49 241 9809418-0, Fax: -9
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