linux-kernel - [PATCH v2] FS-Cache: fix buffer size for decimal value of special cookie type

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Date:   Wed, 26 Apr 2017 20:31:38 -0400
From:   Jérémy Lefaure 
        <jeremy.lefaure@....epita.fr>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        David Howells <dhowells@...hat.com>
Cc:     linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-cachefs@...hat.com, linux-kernel@...r.kernel.org,
        Jérémy Lefaure 
        <jeremy.lefaure@....epita.fr>
Subject: [PATCH v2] FS-Cache: fix buffer size for decimal value of special cookie type

When building object-list.o, gcc (version 7) raises a warning on the
sprintf call in fscache_objlist_show:

  CC      fs/fscache/object-list.o
fs/fscache/object-list.c: In function ‘fscache_objlist_show’:
fs/fscache/object-list.c:265:19: warning: ‘sprintf’ may write a
terminating nul past the end of the destination [-Wformat-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
    sprintf(_type, "%02u", cookie->def->type);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Moreover, the documentation says that value for special cookies is a
hexadecimal value (see Documentation/filesystems/caching/fscache.txt).

Increasing the buffer size to use a decimal value fixes the problem
without any effect on userland tools. Also, this patch updates the
documentation.

Signed-off-by: Jérémy Lefaure <jeremy.lefaure@....epita.fr>
---
v2:
_ keep decimal value
_ fix _type buffer size
_ fix documentation

I didn't have the time to test this patch yet but everything should be fine.


 Documentation/filesystems/caching/fscache.txt |  2 +-
 fs/fscache/object-list.c                      | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Documentation/filesystems/caching/fscache.txt b/Documentation/filesystems/caching/fscache.txt
index 50f0a5757f48..9c3df61b3c16 100644
--- a/Documentation/filesystems/caching/fscache.txt
+++ b/Documentation/filesystems/caching/fscache.txt
@@ -374,7 +374,7 @@ and the second set of columns describe the object's cookie, if present:
 	COLUMN		DESCRIPTION
 	===============	=======================================================
 	NETFS_COOKIE_DEF Name of netfs cookie definition
-	TY		Cookie type (IX - index, DT - data, hex - special)
+	TY		Cookie type (IX - index, DT - data, decimal - special)
 	FL		Cookie flags
 	NETFS_DATA	Netfs private data stored in the cookie
 	OBJECT_KEY	Object key	} 1 column, with separating comma
diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 67f940892ef8..3452d7dbf1e1 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -169,7 +169,7 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
 	struct fscache_object *obj = v;
 	struct fscache_cookie *cookie;
 	unsigned long config = data->config;
-	char _type[3], *type;
+	char _type[4], *type;
 	u8 *buf = data->buf, *p;
 
 	if ((unsigned long) v == 1) {
@@ -194,7 +194,7 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
 	if ((unsigned long) v == 2) {
 		seq_puts(m, "======== ======== ==== ===== === === === == ====="
 			 " == == == ="
-			 " | ================ == == ================");
+			 " | ================ === == ================");
 		if (config & (FSCACHE_OBJLIST_CONFIG_KEY |
 			      FSCACHE_OBJLIST_CONFIG_AUX))
 			seq_puts(m, " ================");
@@ -256,13 +256,13 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
 
 		switch (cookie->def->type) {
 		case 0:
-			type = "IX";
+			type = " IX";
 			break;
 		case 1:
-			type = "DT";
+			type = " DT";
 			break;
 		default:
-			sprintf(_type, "%02u", cookie->def->type);
+			sprintf(_type, "%03u", cookie->def->type);
 			type = _type;
 			break;
 		}
-- 
2.12.2