[PATCH 3/3] NFS: Detect loops in a readdir due to bad cookies

[Bryan Schumaker <bjschuma@netapp.com>]

Some filesystems (such as ext4) can return the same cookie value for multiple
files.  If we try to start a readdir with one of these cookies, the server will
return the first file found with a cookie of the same value.  This can cause 
the client to enter an infinite loop.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
---
 fs/nfs/dir.c           |   23 ++++++++++++++++++++++-
 include/linux/nfs_fs.h |    2 ++
 2 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index b503791..dc475a7 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -139,7 +139,9 @@ static struct nfs_open_dir_context *alloc_nfs_open_dir_context(struct rpc_cred *
 	struct nfs_open_dir_context *ctx;
 	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 	if (ctx != NULL) {
+		ctx->duped = 0;
 		ctx->dir_cookie = 0;
+		ctx->dup_cookie = 0;
 		ctx->cred = get_rpccred(cred);
 	}
 	return ctx;
@@ -342,11 +344,18 @@ static
 int nfs_readdir_search_for_cookie(struct nfs_cache_array *array, nfs_readdir_descriptor_t *desc)
 {
 	int i;
+	int new_pos;
 	int status = -EAGAIN;
+	struct nfs_open_dir_context *ctx = desc->file->private_data;
 
 	for (i = 0; i < array->size; i++) {
 		if (array->array[i].cookie == *desc->dir_cookie) {
-			desc->file->f_pos = desc->current_index + i;
+			new_pos = desc->current_index + i;
+			if (new_pos < desc->file->f_pos) {
+				ctx->dup_cookie = *desc->dir_cookie;
+				ctx->duped = 1;
+			}
+			desc->file->f_pos = new_pos;
 			desc->cache_entry_index = i;
 			return 0;
 		}
@@ -731,6 +740,18 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
 	int i = 0;
 	int res = 0;
 	struct nfs_cache_array *array = NULL;
+	struct nfs_open_dir_context *ctx = file->private_data;
+
+	if (ctx->duped == 1 && ctx->dup_cookie == *desc->dir_cookie) {
+		if (printk_ratelimit()) {
+			pr_notice("NFS: directory %s/%s contains a readdir loop.  "
+				"Please contact your server vendor.",
+				file->f_dentry->d_parent->d_name.name,
+				file->f_dentry->d_name.name);
+		}
+		res = -ELOOP;
+		goto out;
+	}
 
 	array = nfs_readdir_get_array(desc->page);
 	if (IS_ERR(array)) {
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 4b87c00..bbb812b 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -97,7 +97,9 @@ struct nfs_open_context {
 
 struct nfs_open_dir_context {
 	struct rpc_cred *cred;
+	int duped;
 	__u64 dir_cookie;
+	__u64 dup_cookie;
 };
 
 /*
-- 
1.7.4.1