linux-kernel - [PATCH 3.16 155/178] cifs: Do not send echoes before Negotiate is complete

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Message-ID: <lsq.1500213406.158777372@decadent.org.uk>
Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jonathan Liu" <net147@...il.com>,
        "Sachin Prabhu" <sprabhu@...hat.com>,
        "Steve French" <smfrench@...il.com>,
        "Pavel Shilovsky" <pshilov@...rosoft.com>
Subject: [PATCH 3.16 155/178] cifs: Do not send echoes before Negotiate is
 complete

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Sachin Prabhu <sprabhu@...hat.com>

commit 62a6cfddcc0a5313e7da3e8311ba16226fe0ac10 upstream.

commit 4fcd1813e640 ("Fix reconnect to not defer smb3 session reconnect
long after socket reconnect") added support for Negotiate requests to
be initiated by echo calls.

To avoid delays in calling echo after a reconnect, I added the patch
introduced by the commit b8c600120fc8 ("Call echo service immediately
after socket reconnect").

This has however caused a regression with cifs shares which do not have
support for echo calls to trigger Negotiate requests. On connections
which need to call Negotiation, the echo calls trigger an error which
triggers a reconnect which in turn triggers another echo call. This
results in a loop which is only broken when an operation is performed on
the cifs share. For an idle share, it can DOS a server.

The patch uses the smb_operation can_echo() for cifs so that it is
called only if connection has been already been setup.

kernel bz: 194531

Signed-off-by: Sachin Prabhu <sprabhu@...hat.com>
Tested-by: Jonathan Liu <net147@...il.com>
Acked-by: Pavel Shilovsky <pshilov@...rosoft.com>
Signed-off-by: Steve French <smfrench@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/cifs/smb1ops.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/fs/cifs/smb1ops.c
+++ b/fs/cifs/smb1ops.c
@@ -1015,6 +1015,15 @@ cifs_dir_needs_close(struct cifsFileInfo
 	return !cfile->srch_inf.endOfSearch && !cfile->invalidHandle;
 }

+static bool
+cifs_can_echo(struct TCP_Server_Info *server)
+{
+	if (server->tcpStatus == CifsGood)
+		return true;
+
+	return false;
+}
+
 struct smb_version_operations smb1_operations = {
 	.send_cancel = send_nt_cancel,
 	.compare_fids = cifs_compare_fids,
@@ -1048,6 +1057,7 @@ struct smb_version_operations smb1_opera
 	.get_dfs_refer = CIFSGetDFSRefer,
 	.qfs_tcon = cifs_qfs_tcon,
 	.is_path_accessible = cifs_is_path_accessible,
+	.can_echo = cifs_can_echo,
 	.query_path_info = cifs_query_path_info,
 	.query_file_info = cifs_query_file_info,
 	.get_srv_inum = cifs_get_srv_inum,