[PATCH] NFS: Fix lookup intent handling

We should never apply a lookup intent to anything other than the last
path component in an open(), create() or access() call.

Introduce the helper nfs_lookup_check_intent() which always returns
zero if LOOKUP_CONTINUE or LOOKUP_PARENT are set, and returns the
intent flags if we're on the last component of the lookup.
By doing so, we fix a bug in open(O_EXCL), where we may end up
optimizing away a real lookup of the parent directory.

Problem noticed by Linda Dunaphant <linda.dunaphant@ccur.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 35 insertions, 14 deletions

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 73f96acd5d37..ff6155f5e8d9 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -528,19 +528,39 @@ static inline void nfs_renew_times(struct dentry * dentry)
         dentry->d_time = jiffies;
 }
 
+/*
+ * Return the intent data that applies to this particular path component
+ *
+ * Note that the current set of intents only apply to the very last
+ * component of the path.
+ * We check for this using LOOKUP_CONTINUE and LOOKUP_PARENT.
+ */
+static inline unsigned int nfs_lookup_check_intent(struct nameidata *nd, unsigned int mask)
+{
+        if (nd->flags & (LOOKUP_CONTINUE|LOOKUP_PARENT))
+                return 0;
+        return nd->flags & mask;
+}
+
+/*
+ * Inode and filehandle revalidation for lookups.
+ *
+ * We force revalidation in the cases where the VFS sets LOOKUP_REVAL,
+ * or if the intent information indicates that we're about to open this
+ * particular file and the "nocto" mount flag is not set.
+ *
+ */
 static inline
 int nfs_lookup_verify_inode(struct inode *inode, struct nameidata *nd)
 {
         struct nfs_server *server = NFS_SERVER(inode);
 
         if (nd != NULL) {
-                int ndflags = nd->flags;
                 /* VFS wants an on-the-wire revalidation */
-                if (ndflags & LOOKUP_REVAL)
+                if (nd->flags & LOOKUP_REVAL)
                         goto out_force;
                 /* This is an open(2) */
-                if ((ndflags & LOOKUP_OPEN) &&
-                                !(ndflags & LOOKUP_CONTINUE) &&
+                if (nfs_lookup_check_intent(nd, LOOKUP_OPEN) != 0 &&
                                 !(server->flags & NFS_MOUNT_NOCTO))
                         goto out_force;
         }
@@ -560,12 +580,8 @@ static inline
 int nfs_neg_need_reval(struct inode *dir, struct dentry *dentry,
                        struct nameidata *nd)
 {
-        int ndflags = 0;
-
-        if (nd)
-                ndflags = nd->flags;
         /* Don't revalidate a negative dentry if we're creating a new file */
-        if ((ndflags & LOOKUP_CREATE) && !(ndflags & LOOKUP_CONTINUE))
+        if (nd != NULL && nfs_lookup_check_intent(nd, LOOKUP_CREATE) != 0)
                 return 0;
         return !nfs_check_verifier(dir, dentry);
 }
@@ -700,12 +716,16 @@ struct dentry_operations nfs_dentry_operations = {
         .d_iput         = nfs_dentry_iput,
 };
 
+/*
+ * Use intent information to check whether or not we're going to do
+ * an O_EXCL create using this path component.
+ */
 static inline
 int nfs_is_exclusive_create(struct inode *dir, struct nameidata *nd)
 {
         if (NFS_PROTO(dir)->version == 2)
                 return 0;
-        if (!nd || (nd->flags & LOOKUP_CONTINUE) || !(nd->flags & LOOKUP_CREATE))
+        if (nd == NULL || nfs_lookup_check_intent(nd, LOOKUP_CREATE) == 0)
                 return 0;
         return (nd->intent.open.flags & O_EXCL) != 0;
 }
@@ -772,12 +792,13 @@ struct dentry_operations nfs4_dentry_operations = {
         .d_iput         = nfs_dentry_iput,
 };
 
+/*
+ * Use intent information to determine whether we need to substitute
+ * the NFSv4-style stateful OPEN for the LOOKUP call
+ */
 static int is_atomic_open(struct inode *dir, struct nameidata *nd)
 {
-        if (!nd)
-                return 0;
-        /* Check that we are indeed trying to open this file */
-        if ((nd->flags & LOOKUP_CONTINUE) || !(nd->flags & LOOKUP_OPEN))
+        if (nd == NULL || nfs_lookup_check_intent(nd, LOOKUP_OPEN) == 0)
                 return 0;
         /* NFS does not (yet) have a stateful open for directories */
         if (nd->flags & LOOKUP_DIRECTORY)