cifs: stop trying to use virtual circuits

Currently, we try to ensure that we use vcnum of 0 on the first
established session on a connection and then try to use a different
vcnum on each session after that.

This is a little odd, since there's no real reason to use a different
vcnum for each SMB session. I can only assume there was some confusion
between SMB sessions and VCs. That's somewhat understandable since they
both get created during SESSION_SETUP, but the documentation indicates
that they are really orthogonal. The comment on max_vcs in particular
looks quite misguided. An SMB session is already uniquely identified
by the SMB UID value -- there's no need to again uniquely ID with a
VC.

Furthermore, a vcnum of 0 is a cue to the server that it should release
any resources that were previously held by the client. This sounds like
a good thing, until you consider that:

a) it totally ignores the fact that other programs on the box (e.g.
smbclient) might have connections established to the server. Using a
vcnum of 0 causes them to get kicked off.

b) it causes problems with NAT. If several clients are connected to the
same server via the same NAT'ed address, whenever one connects to the
server it kicks off all the others, which then reconnect and kick off
the first one...ad nauseum.

I don't see any reason to ignore the advice in "Implementing CIFS" which
has a comprehensive treatment of virtual circuits. In there, it states
"...and contrary to the specs the client should always use a VcNumber of
one, never zero."

Have the client just use a hardcoded vcnum of 1, and stop abusing the
special behavior of vcnum 0.
Reported-by: Sauron99@gmx.de <sauron99@gmx.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Volker Lendecke <vl@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsglob.h

@@ -547,9 +547,6 @@ struct TCP_Server_Info {
 	unsigned int max_rw;	/* maxRw specifies the maximum */
 	/* message size the server can send or receive for */
 	/* SMB_COM_WRITE_RAW or SMB_COM_READ_RAW. */
-	unsigned int max_vcs;	/* maximum number of smb sessions, at least
-				   those that can be specified uniquely with
-				   vcnumbers */
 	unsigned int capabilities; /* selective disabling of caps by smb sess */
 	int timeAdj;  /* Adjust for difference in server time zone in sec */
 	__u64 CurrentMid;         /* multiplex id - rotating counter */
@@ -715,7 +712,6 @@ struct cifs_ses {
 	enum statusEnum status;
 	unsigned overrideSecFlg;  /* if non-zero override global sec flags */
 	__u16 ipc_tid;		/* special tid for connection to IPC share */
-	__u16 vcnum;
 	char *serverOS;		/* name of operating system underlying server */
 	char *serverNOS;	/* name of network operating system of server */
 	char *serverDomain;	/* security realm of server */

fs/cifs/cifssmb.c

@@ -463,7 +463,6 @@ decode_lanman_negprot_rsp(struct TCP_Server_Info *server, NEGOTIATE_RSP *pSMBr)
 			       cifs_max_pending);
 	set_credits(server, server->maxReq);
 	server->maxBuf = le16_to_cpu(rsp->MaxBufSize);
-	server->max_vcs = le16_to_cpu(rsp->MaxNumberVcs);
 	/* even though we do not use raw we might as well set this
 	accurately, in case we ever find a need for it */
 	if ((le16_to_cpu(rsp->RawMode) & RAW_ENABLE) == RAW_ENABLE) {

fs/cifs/sess.c

@@ -32,88 +32,6 @@
 #include <linux/slab.h>
 #include "cifs_spnego.h"
 
-/*
- * Checks if this is the first smb session to be reconnected after
- * the socket has been reestablished (so we know whether to use vc 0).
- * Called while holding the cifs_tcp_ses_lock, so do not block
- */
-static bool is_first_ses_reconnect(struct cifs_ses *ses)
-{
-	struct list_head *tmp;
-	struct cifs_ses *tmp_ses;
-
-	list_for_each(tmp, &ses->server->smb_ses_list) {
-		tmp_ses = list_entry(tmp, struct cifs_ses,
-				     smb_ses_list);
-		if (tmp_ses->need_reconnect == false)
-			return false;
-	}
-	/* could not find a session that was already connected,
-	   this must be the first one we are reconnecting */
-	return true;
-}
-
-/*
- *	vc number 0 is treated specially by some servers, and should be the
- *      first one we request.  After that we can use vcnumbers up to maxvcs,
- *	one for each smb session (some Windows versions set maxvcs incorrectly
- *	so maxvc=1 can be ignored).  If we have too many vcs, we can reuse
- *	any vc but zero (some servers reset the connection on vcnum zero)
- *
- */
-static __le16 get_next_vcnum(struct cifs_ses *ses)
-{
-	__u16 vcnum = 0;
-	struct list_head *tmp;
-	struct cifs_ses *tmp_ses;
-	__u16 max_vcs = ses->server->max_vcs;
-	__u16 i;
-	int free_vc_found = 0;
-
-	/* Quoting the MS-SMB specification: "Windows-based SMB servers set this
-	field to one but do not enforce this limit, which allows an SMB client
-	to establish more virtual circuits than allowed by this value ... but
-	other server implementations can enforce this limit." */
-	if (max_vcs < 2)
-		max_vcs = 0xFFFF;
-
-	spin_lock(&cifs_tcp_ses_lock);
-	if ((ses->need_reconnect) && is_first_ses_reconnect(ses))
-			goto get_vc_num_exit;  /* vcnum will be zero */
-	for (i = ses->server->srv_count - 1; i < max_vcs; i++) {
-		if (i == 0) /* this is the only connection, use vc 0 */
-			break;
-
-		free_vc_found = 1;
-
-		list_for_each(tmp, &ses->server->smb_ses_list) {
-			tmp_ses = list_entry(tmp, struct cifs_ses,
-					     smb_ses_list);
-			if (tmp_ses->vcnum == i) {
-				free_vc_found = 0;
-				break; /* found duplicate, try next vcnum */
-			}
-		}
-		if (free_vc_found)
-			break; /* we found a vcnumber that will work - use it */
-	}
-
-	if (i == 0)
-		vcnum = 0; /* for most common case, ie if one smb session, use
-			      vc zero.  Also for case when no free vcnum, zero
-			      is safest to send (some clients only send zero) */
-	else if (free_vc_found == 0)
-		vcnum = 1;  /* we can not reuse vc=0 safely, since some servers
-				reset all uids on that, but 1 is ok. */
-	else
-		vcnum = i;
-	ses->vcnum = vcnum;
-get_vc_num_exit:
-	spin_unlock(&cifs_tcp_ses_lock);
-
-	return cpu_to_le16(vcnum);
-}
-
 static __u32 cifs_ssetup_hdr(struct cifs_ses *ses, SESSION_SETUP_ANDX *pSMB)
 {
 	__u32 capabilities = 0;
@@ -128,7 +46,7 @@ static __u32 cifs_ssetup_hdr(struct cifs_ses *ses, SESSION_SETUP_ANDX *pSMB)
 					CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4,
 					USHRT_MAX));
 	pSMB->req.MaxMpxCount = cpu_to_le16(ses->server->maxReq);
-	pSMB->req.VcNumber = get_next_vcnum(ses);
+	pSMB->req.VcNumber = __constant_cpu_to_le16(1);
 
 	/* Now no need to set SMBFLG_CASELESS or obsolete CANONICAL PATH */