cifs: add spinlock for the openFileList to cifsInodeInfo

We can not depend on the tcon->open_file_lock here since in multiuser mode
we may have the same file/inode open via multiple different tcons.

The current code is race prone and will crash if one user deletes a file
at the same time a different user opens/create the file.

To avoid this we need to have a spinlock attached to the inode and not the tcon.

RHBZ:  1580165

CC: Stable <stable@vger.kernel.org>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifsfs.c

@@ -303,6 +303,7 @@ cifs_alloc_inode(struct super_block *sb)
 	cifs_inode->uniqueid = 0;
 	cifs_inode->createtime = 0;
 	cifs_inode->epoch = 0;
+	spin_lock_init(&cifs_inode->open_file_lock);
 	generate_random_uuid(cifs_inode->lease_key);
 
 	/*

fs/cifs/cifsglob.h

@@ -1377,6 +1377,7 @@ struct cifsInodeInfo {
 	struct rw_semaphore lock_sem;	/* protect the fields above */
 	/* BB add in lists for dirty pages i.e. write caching info for oplock */
 	struct list_head openFileList;
+	spinlock_t	open_file_lock;	/* protects openFileList */
 	__u32 cifsAttrs; /* e.g. DOS archive bit, sparse, compressed, system */
 	unsigned int oplock;		/* oplock/lease level we have */
 	unsigned int epoch;		/* used to track lease state changes */
@@ -1780,10 +1781,14 @@ require use of the stronger protocol */
  *  tcp_ses_lock protects:
  *	list operations on tcp and SMB session lists
  *  tcon->open_file_lock protects the list of open files hanging off the tcon
+ *  inode->open_file_lock protects the openFileList hanging off the inode
  *  cfile->file_info_lock protects counters and fields in cifs file struct
  *  f_owner.lock protects certain per file struct operations
  *  mapping->page_lock protects certain per page operations
  *
+ *  Note that the cifs_tcon.open_file_lock should be taken before
+ *  not after the cifsInodeInfo.open_file_lock
+ *
  *  Semaphores
  *  ----------
  *  sesSem     operations on smb session

fs/cifs/file.c

@@ -338,10 +338,12 @@ cifs_new_fileinfo(struct cifs_fid *fid, struct file *file,
 	atomic_inc(&tcon->num_local_opens);
 
 	/* if readable file instance put first in list*/
+	spin_lock(&cinode->open_file_lock);
 	if (file->f_mode & FMODE_READ)
 		list_add(&cfile->flist, &cinode->openFileList);
 	else
 		list_add_tail(&cfile->flist, &cinode->openFileList);
+	spin_unlock(&cinode->open_file_lock);
 	spin_unlock(&tcon->open_file_lock);
 
 	if (fid->purge_cache)
@@ -413,7 +415,9 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 	cifs_add_pending_open_locked(&fid, cifs_file->tlink, &open);
 
 	/* remove it from the lists */
+	spin_lock(&cifsi->open_file_lock);
 	list_del(&cifs_file->flist);
+	spin_unlock(&cifsi->open_file_lock);
 	list_del(&cifs_file->tlist);
 	atomic_dec(&tcon->num_local_opens);
 
@@ -1950,9 +1954,9 @@ refind_writable:
 			return 0;
 		}
 
-		spin_lock(&tcon->open_file_lock);
+		spin_lock(&cifs_inode->open_file_lock);
 		list_move_tail(&inv_file->flist, &cifs_inode->openFileList);
-		spin_unlock(&tcon->open_file_lock);
+		spin_unlock(&cifs_inode->open_file_lock);
 		cifsFileInfo_put(inv_file);
 		++refind;
 		inv_file = NULL;