NFS: Ensure we revalidate attributes before using execute_ok()

Donald Buczek reports that NFS clients can also report incorrect
results for access() due to lack of revalidation of attributes
before calling execute_ok().
Looking closely, it seems chdir() is afflicted with the same problem.

Fix is to ensure we call nfs_revalidate_inode_rcu() or
nfs_revalidate_inode() as appropriate before deciding to trust
execute_ok().

Reported-by: Donald Buczek <buczek@molgen.mpg.de>
Link: http://lkml.kernel.org/r/1451331530-3748-1-git-send-email-buczek@molgen.mpg.de
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 44e519c21e18..5bd2f5bfaf57 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2432,6 +2432,20 @@ int nfs_may_open(struct inode *inode, struct rpc_cred *cred, int openflags)
 }
 EXPORT_SYMBOL_GPL(nfs_may_open);
 
+static int nfs_execute_ok(struct inode *inode, int mask)
+{
+        struct nfs_server *server = NFS_SERVER(inode);
+        int ret;
+
+        if (mask & MAY_NOT_BLOCK)
+                ret = nfs_revalidate_inode_rcu(server, inode);
+        else
+                ret = nfs_revalidate_inode(server, inode);
+        if (ret == 0 && !execute_ok(inode))
+                ret = -EACCES;
+        return ret;
+}
+
 int nfs_permission(struct inode *inode, int mask)
 {
         struct rpc_cred *cred;
@@ -2484,8 +2498,8 @@ force_lookup:
                         res = PTR_ERR(cred);
         }
 out:
-        if (!res && (mask & MAY_EXEC) && !execute_ok(inode))
-                res = -EACCES;
+        if (!res && (mask & MAY_EXEC))
+                res = nfs_execute_ok(inode, mask);
 
         dfprintk(VFS, "NFS: permission(%s/%lu), mask=0x%x, res=%d\n",
                 inode->i_sb->s_id, inode->i_ino, mask, res);