[PATCH][SMB3] do not negotiate compression information unless explicitly requested by user at mount

[Steve French <smfrench@gmail.com>]

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Since in theory a server could respond with compressed read
responses even if not requested on read request (assuming that
a compression negcontext is sent in negotiate protocol) - do
not send compression information during negotiate protocol
unless the user asks for compression explicitly (compression
is experimental), and add a mount warning that compression
is experimental.



-- 
Thanks,

Steve

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From 3d635d89bde9ea033ac72178053abf668c937268 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Mon, 24 Jun 2019 20:39:04 -0500
Subject: [PATCH] smb3: do not send compression info by default

Since in theory a server could respond with compressed read
responses even if not requested on read request (assuming that
a compression negcontext is sent in negotiate protocol) - do
not send compression information during negotiate protocol
unless the user asks for compression explicitly (compression
is experimental), and add a mount warning that compression
is experimental.

Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/cifsglob.h |  1 +
 fs/cifs/connect.c  |  8 ++++++++
 fs/cifs/smb2pdu.c  | 22 ++++++++++++----------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 90867264ba4e..dd99d0318b77 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -601,6 +601,7 @@ struct smb_vol {
 	__u64 snapshot_time; /* needed for timewarp tokens */
 	__u32 handle_timeout; /* persistent and durable handle timeout in ms */
 	unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
+	__u16 compression; /* compression algorithm 0xFFFF default 0=disabled */
 };
 
 /**
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 54e2b2652c3d..da85a251a609 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -97,6 +97,7 @@ enum {
 	Opt_persistent, Opt_nopersistent,
 	Opt_resilient, Opt_noresilient,
 	Opt_domainauto, Opt_rdma, Opt_modeace,
+	Opt_compress,
 
 	/* Mount options which take numeric value */
 	Opt_backupuid, Opt_backupgid, Opt_uid,
@@ -213,6 +214,7 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_echo_interval, "echo_interval=%s" },
 	{ Opt_max_credits, "max_credits=%s" },
 	{ Opt_snapshot, "snapshot=%s" },
+	{ Opt_compress, "compress=%s" },
 
 	{ Opt_blank_user, "user=" },
 	{ Opt_blank_user, "username=" },
@@ -1915,6 +1917,11 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 		case Opt_rdma:
 			vol->rdma = true;
 			break;
+		case Opt_compress:
+			vol->compression = UNKNOWN_TYPE;
+			cifs_dbg(VFS,
+				"SMB3 compression support is experimental\n");
+			break;
 
 		/* Numeric Values */
 		case Opt_backupuid:
@@ -2691,6 +2698,7 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
 	tcp_ses->sequence_number = 0;
 	tcp_ses->reconnect_instance = 1;
 	tcp_ses->lstrp = jiffies;
+	tcp_ses->compress_algorithm = cpu_to_le16(volume_info->compression);
 	spin_lock_init(&tcp_ses->req_lock);
 	INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
 	INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index ab3300a39071..8e289404f6b0 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -521,7 +521,7 @@ build_posix_ctxt(struct smb2_posix_neg_context *pneg_ctxt)
 
 static void
 assemble_neg_contexts(struct smb2_negotiate_req *req,
-		      unsigned int *total_len)
+		      struct TCP_Server_Info *server, unsigned int *total_len)
 {
 	char *pneg_ctxt = (char *)req;
 	unsigned int ctxt_len;
@@ -551,17 +551,19 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 	*total_len += ctxt_len;
 	pneg_ctxt += ctxt_len;
 
-	build_compression_ctxt((struct smb2_compression_capabilities_context *)
+	if (server->compress_algorithm) {
+		build_compression_ctxt((struct smb2_compression_capabilities_context *)
 				pneg_ctxt);
-	ctxt_len = DIV_ROUND_UP(
-		sizeof(struct smb2_compression_capabilities_context), 8) * 8;
-	*total_len += ctxt_len;
-	pneg_ctxt += ctxt_len;
-
+		ctxt_len = DIV_ROUND_UP(
+			sizeof(struct smb2_compression_capabilities_context),
+				8) * 8;
+		*total_len += ctxt_len;
+		pneg_ctxt += ctxt_len;
+		req->NegotiateContextCount = cpu_to_le16(4);
+	} else
+		req->NegotiateContextCount = cpu_to_le16(3);
 	build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
 	*total_len += sizeof(struct smb2_posix_neg_context);
-
-	req->NegotiateContextCount = cpu_to_le16(4);
 }
 
 static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
@@ -829,7 +831,7 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 		if ((ses->server->vals->protocol_id == SMB311_PROT_ID) ||
 		    (strcmp(ses->server->vals->version_string,
 		     SMBDEFAULT_VERSION_STRING) == 0))
-			assemble_neg_contexts(req, &total_len);
+			assemble_neg_contexts(req, server, &total_len);
 	}
 	iov[0].iov_base = (char *)req;
 	iov[0].iov_len = total_len;
-- 
2.20.1