linux-kernel - [PATCH 21/22] fscache: fix fscache_objlist

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Message-Id: <20170714120720.906842-22-arnd@arndb.de>
Date:   Fri, 14 Jul 2017 14:07:13 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>, akpm@...ux-foundation.org,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>,
        James Morris <james.l.morris@...cle.com>,
        linux-cachefs@...hat.com
Subject: [PATCH 21/22] fscache: fix fscache_objlist_show format processing

gcc points out a minor bug in the handling of unknown
cookie types, which could result in a string overflow
when the integer is copied into a 3-byte string:

fs/fscache/object-list.c: In function 'fscache_objlist_show':
fs/fscache/object-list.c:265:19: error: 'sprintf' may write a terminating nul past the end of the destination [-Werror=format-overflow=]
 sprintf(_type, "%02u", cookie->def->type);
                ^~~~~~
fs/fscache/object-list.c:265:4: note: 'sprintf' output between 3 and 4 bytes into a destination of size 3

This is currently harmless as no code sets a type other
than 0 or 1, but it makes sense to use snprintf() here
to avoid overflowing the array if that changes.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/fscache/object-list.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 67f940892ef8..b5ab06fabc60 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -262,7 +262,8 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
 			type = "DT";
 			break;
 		default:
-			sprintf(_type, "%02u", cookie->def->type);
+			snprintf(_type, sizeof(_type), "%02u",
+				 cookie->def->type);
 			type = _type;
 			break;
 		}
-- 
2.9.0