[PATCH 4.4 112/137] nfs: use file_dentry()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@xxxxxxxxxx>

commit be62a1a8fd116f5cd9e53726601f970e16e17558 upstream.

NFS may be used as lower layer of overlayfs and accessing f_path.dentry can
lead to a crash.

Fix by replacing direct access of file->f_path.dentry with the
file_dentry() accessor, which will always return a native object.

Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Tested-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Acked-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/nfs/dir.c      |    6 +++---
 fs/nfs/inode.c    |    2 +-
 fs/nfs/nfs4file.c |    4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -377,7 +377,7 @@ int nfs_readdir_xdr_filler(struct page *
  again:
 	timestamp = jiffies;
 	gencount = nfs_inc_attr_generation_counter();
-	error = NFS_PROTO(inode)->readdir(file->f_path.dentry, cred, entry->cookie, pages,
+	error = NFS_PROTO(inode)->readdir(file_dentry(file), cred, entry->cookie, pages,
 					  NFS_SERVER(inode)->dtsize, desc->plus);
 	if (error < 0) {
 		/* We requested READDIRPLUS, but the server doesn't grok it */
@@ -560,7 +560,7 @@ int nfs_readdir_page_filler(nfs_readdir_
 		count++;
 
 		if (desc->plus != 0)
-			nfs_prime_dcache(desc->file->f_path.dentry, entry);
+			nfs_prime_dcache(file_dentry(desc->file), entry);
 
 		status = nfs_readdir_add_to_array(entry, page);
 		if (status != 0)
@@ -864,7 +864,7 @@ static bool nfs_dir_mapping_need_revalid
  */
 static int nfs_readdir(struct file *file, struct dir_context *ctx)
 {
-	struct dentry	*dentry = file->f_path.dentry;
+	struct dentry	*dentry = file_dentry(file);
 	struct inode	*inode = d_inode(dentry);
 	nfs_readdir_descriptor_t my_desc,
 			*desc = &my_desc;
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -927,7 +927,7 @@ int nfs_open(struct inode *inode, struct
 {
 	struct nfs_open_context *ctx;
 
-	ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+	ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 	nfs_file_set_open_context(filp, ctx);
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -26,7 +26,7 @@ static int
 nfs4_file_open(struct inode *inode, struct file *filp)
 {
 	struct nfs_open_context *ctx;
-	struct dentry *dentry = filp->f_path.dentry;
+	struct dentry *dentry = file_dentry(filp);
 	struct dentry *parent = NULL;
 	struct inode *dir;
 	unsigned openflags = filp->f_flags;
@@ -57,7 +57,7 @@ nfs4_file_open(struct inode *inode, stru
 	parent = dget_parent(dentry);
 	dir = d_inode(parent);
 
-	ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+	ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
 	err = PTR_ERR(ctx);
 	if (IS_ERR(ctx))
 		goto out;