[NFS] [PATCH] nfs: Fix NFS v4 client handling of MAY_EXEC in nfs_permission.

[NFS] [PATCH] nfs: Fix NFS v4 client handling of MAY_EXEC in nfs_permission.

[Frank Filz]

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@us.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:
-- 
1.5.2.2




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Re: [PATCH] nfs: Fix NFS v4 client handling of MAY_EXEC in nfs_permission.

[Eugene Teo]

Frank Filz wrote:
> 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 at us.ibm.com>

Tested-by: Eugene Teo <eugeneteo@kernel.sg>

I have tested this on 2.6.29.3, and I can confirm that the patch fixed
the problem.

Btw, this looks like the same problem that was reported in 2006:
http://linux-nfs.org/pipermail/nfsv4/2006-November/005323.html
http://linux-nfs.org/pipermail/nfsv4/2006-November/005313.html
http://bugzilla.linux-nfs.org/show_bug.cgi?id=131

Thanks, Eugene
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