linux-kernel - [PATCH] nfs: Fix NFS v4 client handling of MAY_EXEC in nfs

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Date:	Mon, 18 May 2009 12:29:43 -0700
From:	Frank Filz <ffilzlnx@...ibm.com>
To:	NFS List <linux-nfs@...r.kernel.org>,
	NFS V4 Mailing List <nfsv4@...ux-nfs.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Eugene Teo <eugene@...hat.com>, security@...nel.org,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Bruce Fields <bfields@...ldses.org>
Subject: [PATCH] nfs: Fix NFS v4 client handling of MAY_EXEC in 
	nfs_permission.

Sorry for the resend, got lkml address wrong...

The problem is that permission checking is skipped if atomic open is
possible, but when exec opens a file, it just opens it O_READONLY which
means EXEC permission will not be checked at that time.

This problem is observed by the following sequence (executed as root):

mount -t nfs4 server:/ /mnt4
echo "ls" >/mnt4/foo
chmod 744 /mnt4/foo
su guest -c "mnt4/foo"

Signed-off-by: Frank Filz <ffilzlnx@...ibm.com>
---
 fs/nfs/dir.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 370b190..89f98e9 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1943,7 +1943,8 @@ int nfs_permission(struct inode *inode, int mask)
 		case S_IFREG:
 			/* NFSv4 has atomic_open... */
 			if (nfs_server_capable(inode, NFS_CAP_ATOMIC_OPEN)
-					&& (mask & MAY_OPEN))
+					&& (mask & MAY_OPEN)
+					&& !(mask & MAY_EXEC))
 				goto out;
 			break;
 		case S_IFDIR:

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