[PATCH] cifs: fix mount on old smb servers

[Paulo Alcantara <pc@manguebit.com>]

The client was sending rfc1002 session request packet with a wrong
length field set, therefore failing to mount shares against old SMB
servers over port 139.

Fix this by calculating the correct length as specified in rfc1002.

Fixes: d7173623bf0b ("cifs: use ALIGN() and round_up() macros")
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
---
 fs/cifs/connect.c | 100 ++++++++++++++++++----------------------------
 1 file changed, 38 insertions(+), 62 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index b2a04b4e89a5..af49ae53aaf4 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2843,72 +2843,48 @@ ip_rfc1001_connect(struct TCP_Server_Info *server)
 	 * negprot - BB check reconnection in case where second
 	 * sessinit is sent but no second negprot
 	 */
-	struct rfc1002_session_packet *ses_init_buf;
-	unsigned int req_noscope_len;
-	struct smb_hdr *smb_buf;
+	struct rfc1002_session_packet req = {};
+	struct smb_hdr *smb_buf = (struct smb_hdr *)&req;
+	unsigned int len;
+
+	req.trailer.session_req.called_len = sizeof(req.trailer.session_req.called_name);
+
+	if (server->server_RFC1001_name[0] != 0)
+		rfc1002mangle(req.trailer.session_req.called_name,
+			      server->server_RFC1001_name,
+			      RFC1001_NAME_LEN_WITH_NULL);
+	else
+		rfc1002mangle(req.trailer.session_req.called_name,
+			      DEFAULT_CIFS_CALLED_NAME,
+			      RFC1001_NAME_LEN_WITH_NULL);
+
+	req.trailer.session_req.calling_len = sizeof(req.trailer.session_req.calling_name);
+
+	/* calling name ends in null (byte 16) from old smb convention */
+	if (server->workstation_RFC1001_name[0] != 0)
+		rfc1002mangle(req.trailer.session_req.calling_name,
+			      server->workstation_RFC1001_name,
+			      RFC1001_NAME_LEN_WITH_NULL);
+	else
+		rfc1002mangle(req.trailer.session_req.calling_name,
+			      "LINUX_CIFS_CLNT",
+			      RFC1001_NAME_LEN_WITH_NULL);
 
-	ses_init_buf = kzalloc(sizeof(struct rfc1002_session_packet),
-			       GFP_KERNEL);
-
-	if (ses_init_buf) {
-		ses_init_buf->trailer.session_req.called_len = 32;
-
-		if (server->server_RFC1001_name[0] != 0)
-			rfc1002mangle(ses_init_buf->trailer.
-				      session_req.called_name,
-				      server->server_RFC1001_name,
-				      RFC1001_NAME_LEN_WITH_NULL);
-		else
-			rfc1002mangle(ses_init_buf->trailer.
-				      session_req.called_name,
-				      DEFAULT_CIFS_CALLED_NAME,
-				      RFC1001_NAME_LEN_WITH_NULL);
-
-		ses_init_buf->trailer.session_req.calling_len = 32;
-
-		/*
-		 * calling name ends in null (byte 16) from old smb
-		 * convention.
-		 */
-		if (server->workstation_RFC1001_name[0] != 0)
-			rfc1002mangle(ses_init_buf->trailer.
-				      session_req.calling_name,
-				      server->workstation_RFC1001_name,
-				      RFC1001_NAME_LEN_WITH_NULL);
-		else
-			rfc1002mangle(ses_init_buf->trailer.
-				      session_req.calling_name,
-				      "LINUX_CIFS_CLNT",
-				      RFC1001_NAME_LEN_WITH_NULL);
-
-		ses_init_buf->trailer.session_req.scope1 = 0;
-		ses_init_buf->trailer.session_req.scope2 = 0;
-		smb_buf = (struct smb_hdr *)ses_init_buf;
-
-		/* sizeof RFC1002_SESSION_REQUEST with no scopes */
-		req_noscope_len = sizeof(struct rfc1002_session_packet) - 2;
+	/*
+	 * As per rfc1002, @len must be the number of bytes that follows the
+	 * length field of a rfc1002 session request payload.
+	 */
+	len = sizeof(req) - offsetof(struct rfc1002_session_packet, trailer.session_req);
 
-		/* == cpu_to_be32(0x81000044) */
-		smb_buf->smb_buf_length =
-			cpu_to_be32((RFC1002_SESSION_REQUEST << 24) | req_noscope_len);
-		rc = smb_send(server, smb_buf, 0x44);
-		kfree(ses_init_buf);
-		/*
-		 * RFC1001 layer in at least one server
-		 * requires very short break before negprot
-		 * presumably because not expecting negprot
-		 * to follow so fast.  This is a simple
-		 * solution that works without
-		 * complicating the code and causes no
-		 * significant slowing down on mount
-		 * for everyone else
-		 */
-		usleep_range(1000, 2000);
-	}
+	smb_buf->smb_buf_length = cpu_to_be32((RFC1002_SESSION_REQUEST << 24) | len);
+	rc = smb_send(server, smb_buf, len);
 	/*
-	 * else the negprot may still work without this
-	 * even though malloc failed
+	 * RFC1001 layer in at least one server requires very short break before
+	 * negprot presumably because not expecting negprot to follow so fast.
+	 * This is a simple solution that works without complicating the code
+	 * and causes no significant slowing down on mount for everyone else
 	 */
+	usleep_range(1000, 2000);
 
 	return rc;
 }
-- 
2.39.1