[CIFS] Fix multiuser mounts so server does not invalidate earlier security contexts

When two different users mount the same Windows 2003 Server share using CIFS,
the first session mounted can be invalidated.  Some servers invalidate the first
smb session when a second similar user (e.g. two users who get mapped by server to "guest")
authenticates an smb session from the same client.

By making sure that we set the 2nd and subsequent vc numbers to nonzero values,
this ensures that we will not have this problem.

Fixes Samba bug 6004, problem description follows:
How to reproduce:

- configure an "open share" (full permissions to Guest user) on Windows 2003
Server (I couldn't reproduce the problem with Samba server or Windows older
than 2003)
- mount the share twice with different users who will be authenticated as guest.

 noacl,noperm,user=john,dir_mode=0700,domain=DOMAIN,rw
 noacl,noperm,user=jeff,dir_mode=0700,domain=DOMAIN,rw

Result:

- just the mount point mounted last is accessible:

Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 94c1ca0ec953..e004f6db5fc8 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -164,9 +164,12 @@ struct TCP_Server_Info {
         /* multiplexed reads or writes */
         unsigned int maxBuf;    /* maxBuf specifies the maximum */
         /* message size the server can send or receive for non-raw SMBs */
-        unsigned int maxRw;     /* maxRw specifies the maximum */
+        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 */
         char sessid[4];         /* unique token id for this session */
         /* (returned on Negotiate */
         int capabilities; /* allow selective disabling of caps by smb sess */
@@ -210,6 +213,7 @@ struct cifsSesInfo {
         unsigned overrideSecFlg;  /* if non-zero override global sec flags */
         __u16 ipc_tid;          /* special tid for connection to IPC share */
         __u16 flags;
+        __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 */