ceph: protect access to d_parent

d_parent is protected by d_lock: use it when looking up a dentry's parent
directory inode.  Also take a reference and drop it in the caller to avoid
a use-after-free.
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/dir.c

@@ -71,6 +71,21 @@ int ceph_init_dentry(struct dentry *dentry)
 	return 0;
 }
 
+struct inode *ceph_get_dentry_parent_inode(struct dentry *dentry)
+{
+	struct inode *inode = NULL;
+
+	if (!dentry)
+		return NULL;
+
+	spin_lock(&dentry->d_lock);
+	if (dentry->d_parent) {
+		inode = dentry->d_parent->d_inode;
+		ihold(inode);
+	}
+	spin_unlock(&dentry->d_lock);
+	return inode;
+}
 
 
 /*

fs/ceph/file.c

@@ -122,7 +122,7 @@ int ceph_open(struct inode *inode, struct file *file)
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	struct ceph_mds_request *req;
 	struct ceph_file_info *cf = file->private_data;
-	struct inode *parent_inode = file->f_dentry->d_parent->d_inode;
+	struct inode *parent_inode = NULL;
 	int err;
 	int flags, fmode, wanted;
 
@@ -194,8 +194,10 @@ int ceph_open(struct inode *inode, struct file *file)
 	req->r_inode = inode;
 	ihold(inode);
 	req->r_num_caps = 1;
-	err = ceph_mdsc_do_request(mdsc, (flags & (O_CREAT|O_TRUNC)) ?
-				   parent_inode : NULL, req);
+	if (flags & (O_CREAT|O_TRUNC))
+		parent_inode = ceph_get_dentry_parent_inode(file->f_dentry);
+	err = ceph_mdsc_do_request(mdsc, parent_inode, req);
+	iput(parent_inode);
 	if (!err)
 		err = ceph_init_file(inode, file, req->r_fmode);
 	ceph_mdsc_put_request(req);

fs/ceph/inode.c

@@ -1562,7 +1562,7 @@ int ceph_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	struct inode *inode = dentry->d_inode;
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct inode *parent_inode = dentry->d_parent->d_inode;
+	struct inode *parent_inode;
 	const unsigned int ia_valid = attr->ia_valid;
 	struct ceph_mds_request *req;
 	struct ceph_mds_client *mdsc = ceph_sb_to_client(dentry->d_sb)->mdsc;
@@ -1745,7 +1745,9 @@ int ceph_setattr(struct dentry *dentry, struct iattr *attr)
 		req->r_inode_drop = release;
 		req->r_args.setattr.mask = cpu_to_le32(mask);
 		req->r_num_caps = 1;
+		parent_inode = ceph_get_dentry_parent_inode(dentry);
 		err = ceph_mdsc_do_request(mdsc, parent_inode, req);
+		iput(parent_inode);
 	}
 	dout("setattr %p result=%d (%s locally, %d remote)\n", inode, err,
 	     ceph_cap_string(dirtied), mask);

fs/ceph/ioctl.c

@@ -38,7 +38,7 @@ static long ceph_ioctl_get_layout(struct file *file, void __user *arg)
 static long ceph_ioctl_set_layout(struct file *file, void __user *arg)
 {
 	struct inode *inode = file->f_dentry->d_inode;
-	struct inode *parent_inode = file->f_dentry->d_parent->d_inode;
+	struct inode *parent_inode;
 	struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
 	struct ceph_mds_request *req;
 	struct ceph_ioctl_layout l;
@@ -87,7 +87,9 @@ static long ceph_ioctl_set_layout(struct file *file, void __user *arg)
 	req->r_args.setlayout.layout.fl_pg_preferred =
 		cpu_to_le32(l.preferred_osd);
 
+	parent_inode = ceph_get_dentry_parent_inode(file->f_dentry);
 	err = ceph_mdsc_do_request(mdsc, parent_inode, req);
+	iput(parent_inode);
 	ceph_mdsc_put_request(req);
 	return err;
 }

fs/ceph/super.h

@@ -801,6 +801,7 @@ extern void ceph_dentry_lru_touch(struct dentry *dn);
 extern void ceph_dentry_lru_del(struct dentry *dn);
 extern void ceph_invalidate_dentry_lease(struct dentry *dentry);
 extern unsigned ceph_dentry_hash(struct dentry *dn);
+extern struct inode *ceph_get_dentry_parent_inode(struct dentry *dentry);
 
 /*
  * our d_ops vary depending on whether the inode is live,
@@ -823,14 +824,6 @@ extern int ceph_encode_locks(struct inode *i, struct ceph_pagelist *p,
 			     int p_locks, int f_locks);
 extern int lock_to_ceph_filelock(struct file_lock *fl, struct ceph_filelock *c);
 
-static inline struct inode *get_dentry_parent_inode(struct dentry *dentry)
-{
-	if (dentry && dentry->d_parent)
-		return dentry->d_parent->d_inode;
-
-	return NULL;
-}
-
 /* debugfs.c */
 extern int ceph_fs_debugfs_init(struct ceph_fs_client *client);
 extern void ceph_fs_debugfs_cleanup(struct ceph_fs_client *client);

fs/ceph/xattr.c

@@ -629,7 +629,7 @@ static int ceph_sync_setxattr(struct dentry *dentry, const char *name,
 	struct ceph_fs_client *fsc = ceph_sb_to_client(dentry->d_sb);
 	struct inode *inode = dentry->d_inode;
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct inode *parent_inode = dentry->d_parent->d_inode;
+	struct inode *parent_inode;
 	struct ceph_mds_request *req;
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	int err;
@@ -677,7 +677,9 @@ static int ceph_sync_setxattr(struct dentry *dentry, const char *name,
 	req->r_data_len = size;
 
 	dout("xattr.ver (before): %lld\n", ci->i_xattrs.version);
+	parent_inode = ceph_get_dentry_parent_inode(dentry);
 	err = ceph_mdsc_do_request(mdsc, parent_inode, req);
+	iput(parent_inode);
 	ceph_mdsc_put_request(req);
 	dout("xattr.ver (after): %lld\n", ci->i_xattrs.version);
 
@@ -788,7 +790,7 @@ static int ceph_send_removexattr(struct dentry *dentry, const char *name)
 	struct ceph_fs_client *fsc = ceph_sb_to_client(dentry->d_sb);
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	struct inode *inode = dentry->d_inode;
-	struct inode *parent_inode = dentry->d_parent->d_inode;
+	struct inode *parent_inode;
 	struct ceph_mds_request *req;
 	int err;
 
@@ -802,7 +804,9 @@ static int ceph_send_removexattr(struct dentry *dentry, const char *name)
 	req->r_num_caps = 1;
 	req->r_path2 = kstrdup(name, GFP_NOFS);
 
+	parent_inode = ceph_get_dentry_parent_inode(dentry);
 	err = ceph_mdsc_do_request(mdsc, parent_inode, req);
+	iput(parent_inode);
 	ceph_mdsc_put_request(req);
 	return err;
 }