NFS: nfs_find_open_context() may only select open files

stable inclusion
from linux-4.19.198
commit e409580b19ec7923082e90c1ec9505aa0867f21d

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

[ Upstream commit e97bc663 ]

If a file has already been closed, then it should not be selected to
support further I/O.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
[Trond: Fix an invalid pointer deref reported by Colin Ian King]
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/nfs/inode.c

@@ -1040,6 +1040,7 @@ EXPORT_SYMBOL_GPL(nfs_inode_attach_open_context);
 void nfs_file_set_open_context(struct file *filp, struct nfs_open_context *ctx)
 {
 	filp->private_data = get_nfs_open_context(ctx);
+	set_bit(NFS_CONTEXT_FILE_OPEN, &ctx->flags);
 	if (list_empty(&ctx->list))
 		nfs_inode_attach_open_context(ctx);
 }
@@ -1059,6 +1060,8 @@ struct nfs_open_context *nfs_find_open_context(struct inode *inode, struct rpc_c
 			continue;
 		if ((pos->mode & (FMODE_READ|FMODE_WRITE)) != mode)
 			continue;
+		if (!test_bit(NFS_CONTEXT_FILE_OPEN, &pos->flags))
+			continue;
 		ctx = get_nfs_open_context(pos);
 		break;
 	}
@@ -1073,6 +1076,7 @@ void nfs_file_clear_open_context(struct file *filp)
 	if (ctx) {
 		struct inode *inode = d_inode(ctx->dentry);
 
+		clear_bit(NFS_CONTEXT_FILE_OPEN, &ctx->flags);
 		/*
 		 * We fatal error on write before. Try to writeback
 		 * every page again.

include/linux/nfs_fs.h

@@ -78,6 +78,7 @@ struct nfs_open_context {
 #define NFS_CONTEXT_RESEND_WRITES	(1)
 #define NFS_CONTEXT_BAD			(2)
 #define NFS_CONTEXT_UNLOCK	(3)
+#define NFS_CONTEXT_FILE_OPEN		(4)
 	int error;
 
 	struct list_head list;