cifs: Replace wrtPending with a real reference count

Currently, cifs_close() tries to wait until all I/O is complete and then
frees the file private data.  If I/O does not completely in a reasonable
amount of time it frees the structure anyway, leaving a potential use-
after-free situation.

This patch changes the wrtPending counter to a complete reference count and
lets the last user free the structure.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/file.c

@@ -53,11 +53,9 @@ static inline struct cifsFileInfo *cifs_init_private(
 	private_data->pInode = inode;
 	private_data->invalidHandle = false;
 	private_data->closePend = false;
-	/* we have to track num writers to the inode, since writepages
-	does not tell us which handle the write is for so there can
-	be a close (overlapping with write) of the filehandle that
-	cifs_writepages chose to use */
-	atomic_set(&private_data->wrtPending, 0);
+	/* Initialize reference count to one.  The private data is
+	freed on the release of the last reference */
+	atomic_set(&private_data->count, 1);
 
 	return private_data;
 }
@@ -643,7 +641,7 @@ int cifs_close(struct inode *inode, struct file *file)
 			if (!pTcon->need_reconnect) {
 				write_unlock(&GlobalSMBSeslock);
 				timeout = 2;
-				while ((atomic_read(&pSMBFile->wrtPending) != 0)
+				while ((atomic_read(&pSMBFile->count) != 1)
 					&& (timeout <= 2048)) {
 					/* Give write a better chance to get to
 					server ahead of the close.  We do not
@@ -657,8 +655,6 @@ int cifs_close(struct inode *inode, struct file *file)
 					msleep(timeout);
 					timeout *= 4;
 				}
-				if (atomic_read(&pSMBFile->wrtPending))
-					cERROR(1, ("close with pending write"));
 				if (!pTcon->need_reconnect &&
 				    !pSMBFile->invalidHandle)
 					rc = CIFSSMBClose(xid, pTcon,
@@ -681,24 +677,7 @@ int cifs_close(struct inode *inode, struct file *file)
 		list_del(&pSMBFile->flist);
 		list_del(&pSMBFile->tlist);
 		write_unlock(&GlobalSMBSeslock);
-		timeout = 10;
-		/* We waited above to give the SMBWrite a chance to issue
-		   on the wire (so we do not get SMBWrite returning EBADF
-		   if writepages is racing with close.  Note that writepages
-		   does not specify a file handle, so it is possible for a file
-		   to be opened twice, and the application close the "wrong"
-		   file handle - in these cases we delay long enough to allow
-		   the SMBWrite to get on the wire before the SMB Close.
-		   We allow total wait here over 45 seconds, more than
-		   oplock break time, and more than enough to allow any write
-		   to complete on the server, or to time out on the client */
-		while ((atomic_read(&pSMBFile->wrtPending) != 0)
-				&& (timeout <= 50000)) {
-			cERROR(1, ("writes pending, delay free of handle"));
-			msleep(timeout);
-			timeout *= 8;
-		}
-		kfree(file->private_data);
+		cifsFileInfo_put(file->private_data);
 		file->private_data = NULL;
 	} else
 		rc = -EBADF;
@@ -1236,7 +1215,7 @@ struct cifsFileInfo *find_readable_file(struct cifsInodeInfo *cifs_inode)
 			if (!open_file->invalidHandle) {
 				/* found a good file */
 				/* lock it so it will not be closed on us */
-				atomic_inc(&open_file->wrtPending);
+				cifsFileInfo_get(open_file);
 				read_unlock(&GlobalSMBSeslock);
 				return open_file;
 			} /* else might as well continue, and look for
@@ -1276,7 +1255,7 @@ refind_writable:
 		if (open_file->pfile &&
 		    ((open_file->pfile->f_flags & O_RDWR) ||
 		     (open_file->pfile->f_flags & O_WRONLY))) {
-			atomic_inc(&open_file->wrtPending);
+			cifsFileInfo_get(open_file);
 
 			if (!open_file->invalidHandle) {
 				/* found a good writable file */
@@ -1293,7 +1272,7 @@ refind_writable:
 				else { /* start over in case this was deleted */
 				       /* since the list could be modified */
 					read_lock(&GlobalSMBSeslock);
-					atomic_dec(&open_file->wrtPending);
+					cifsFileInfo_put(open_file);
 					goto refind_writable;
 				}
 			}
@@ -1309,7 +1288,7 @@ refind_writable:
 			read_lock(&GlobalSMBSeslock);
 			/* can not use this handle, no write
 			   pending on this one after all */
-			atomic_dec(&open_file->wrtPending);
+			cifsFileInfo_put(open_file);
 
 			if (open_file->closePend) /* list could have changed */
 				goto refind_writable;
@@ -1373,7 +1352,7 @@ static int cifs_partialpagewrite(struct page *page, unsigned from, unsigned to)
 	if (open_file) {
 		bytes_written = cifs_write(open_file->pfile, write_data,
 					   to-from, &offset);
-		atomic_dec(&open_file->wrtPending);
+		cifsFileInfo_put(open_file);
 		/* Does mm or vfs already set times? */
 		inode->i_atime = inode->i_mtime = current_fs_time(inode->i_sb);
 		if ((bytes_written > 0) && (offset))
@@ -1562,7 +1541,7 @@ retry:
 						   bytes_to_write, offset,
 						   &bytes_written, iov, n_iov,
 						   long_op);
-				atomic_dec(&open_file->wrtPending);
+				cifsFileInfo_put(open_file);
 				cifs_update_eof(cifsi, offset, bytes_written);
 
 				if (rc || bytes_written < bytes_to_write) {