linux-kernel - [PATCH] NFSv4.x: hide array-bounds warning

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Message-Id: <20161122205059.754211-1-arnd@arndb.de>
Date:   Tue, 22 Nov 2016 21:50:52 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Trond Myklebust <trond.myklebust@...marydata.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] NFSv4.x: hide array-bounds warning

A correct bugfix introduced a harmless warning that shows up with gcc-7:

fs/nfs/callback.c: In function 'nfs_callback_up':
fs/nfs/callback.c:214:14: error: array subscript is outside array bounds [-Werror=array-bounds]

What happens here is that the 'minorversion == 0' check tells the
compiler that we assume minorversion can be something other than 0,
but when CONFIG_NFS_V4_1 is disabled that would be invalid and
result in an out-of-bounds access.

The added check for IS_ENABLED(CONFIG_NFS_V4_1) tells gcc that this
really can't happen, which makes the code slightly smaller and also
avoids the warning.

The bugfix that introduced the warning is marked for stable backports,
we want this one backported to the same releases.

Fixes: 98b0f80c2396 ("NFSv4.x: Fix a refcount leak in nfs_callback_up_net")
Cc: stable@...r.kernel.org # v3.7+
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/nfs/callback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 532d8e242d4d..484bebc20bca 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -197,7 +197,7 @@ static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
 	}

 	ret = -EPROTONOSUPPORT;
-	if (minorversion == 0)
+	if (!IS_ENABLED(CONFIG_NFS_V4_1) || minorversion == 0)
 		ret = nfs4_callback_up_net(serv, net);
 	else if (xprt->ops->bc_up)
 		ret = xprt->ops->bc_up(serv, net);
-- 
2.9.0