[CIFS] Ensure that cifs multiplex ids do not collide.
Signed-off-by: Steve French (sfrench@us.ibm.com)
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 20ae415..beeff82 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -34,8 +34,6 @@
extern mempool_t *cifs_req_poolp;
extern struct task_struct * oplockThread;
-static __u16 GlobalMid; /* multiplex id - rotating counter */
-
/* The xid serves as a useful identifier for each incoming vfs request,
in a similar way to the mid which is useful to track each sent smb,
and CurrentXid can also provide a running counter (although it
@@ -51,6 +49,8 @@
GlobalTotalActiveXid++;
if (GlobalTotalActiveXid > GlobalMaxActiveXid)
GlobalMaxActiveXid = GlobalTotalActiveXid; /* keep high water mark for number of simultaneous vfs ops in our filesystem */
+ if(GlobalTotalActiveXid > 65000)
+ cFYI(1,("warning: more than 65000 requests active"));
xid = GlobalCurrentXid++;
spin_unlock(&GlobalMid_Lock);
return xid;
@@ -218,6 +218,76 @@
return;
}
+/*
+ Find a free multiplex id (SMB mid). Otherwise there could be
+ mid collisions which might cause problems, demultiplexing the
+ wrong response to this request. Multiplex ids could collide if
+ one of a series requests takes much longer than the others, or
+ if a very large number of long lived requests (byte range
+ locks or FindNotify requests) are pending. No more than
+ 64K-1 requests can be outstanding at one time. If no
+ mids are available, return zero. A future optimization
+ could make the combination of mids and uid the key we use
+ to demultiplex on (rather than mid alone).
+ In addition to the above check, the cifs demultiplex
+ code already used the command code as a secondary
+ check of the frame and if signing is negotiated the
+ response would be discarded if the mid were the same
+ but the signature was wrong. Since the mid is not put in the
+ pending queue until later (when it is about to be dispatched)
+ we do have to limit the number of outstanding requests
+ to somewhat less than 64K-1 although it is hard to imagine
+ so many threads being in the vfs at one time.
+*/
+__u16 GetNextMid(struct TCP_Server_Info *server)
+{
+ __u16 mid = 0;
+ __u16 last_mid;
+ int collision;
+
+ if(server == NULL)
+ return mid;
+
+ spin_lock(&GlobalMid_Lock);
+ last_mid = server->CurrentMid; /* we do not want to loop forever */
+ server->CurrentMid++;
+ /* This nested loop looks more expensive than it is.
+ In practice the list of pending requests is short,
+ fewer than 50, and the mids are likely to be unique
+ on the first pass through the loop unless some request
+ takes longer than the 64 thousand requests before it
+ (and it would also have to have been a request that
+ did not time out) */
+ while(server->CurrentMid != last_mid) {
+ struct list_head *tmp;
+ struct mid_q_entry *mid_entry;
+
+ collision = 0;
+ if(server->CurrentMid == 0)
+ server->CurrentMid++;
+
+ list_for_each(tmp, &server->pending_mid_q) {
+ mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
+
+ if ((mid_entry->mid == server->CurrentMid) &&
+ (mid_entry->midState == MID_REQUEST_SUBMITTED)) {
+ /* This mid is in use, try a different one */
+ collision = 1;
+ break;
+ }
+ }
+ if(collision == 0) {
+ mid = server->CurrentMid;
+ break;
+ }
+ server->CurrentMid++;
+ }
+ spin_unlock(&GlobalMid_Lock);
+ return mid;
+}
+
+/* NB: MID can not be set if treeCon not passed in, in that
+ case it is responsbility of caller to set the mid */
void
header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
const struct cifsTconInfo *treeCon, int word_count
@@ -233,7 +303,8 @@
(2 * word_count) + sizeof (struct smb_hdr) -
4 /* RFC 1001 length field does not count */ +
2 /* for bcc field itself */ ;
- /* Note that this is the only network field that has to be converted to big endian and it is done just before we send it */
+ /* Note that this is the only network field that has to be converted
+ to big endian and it is done just before we send it */
buffer->Protocol[0] = 0xFF;
buffer->Protocol[1] = 'S';
@@ -245,8 +316,6 @@
buffer->Pid = cpu_to_le16((__u16)current->tgid);
buffer->PidHigh = cpu_to_le16((__u16)(current->tgid >> 16));
spin_lock(&GlobalMid_Lock);
- GlobalMid++;
- buffer->Mid = GlobalMid;
spin_unlock(&GlobalMid_Lock);
if (treeCon) {
buffer->Tid = treeCon->tid;
@@ -256,8 +325,9 @@
if (treeCon->ses->capabilities & CAP_STATUS32) {
buffer->Flags2 |= SMBFLG2_ERR_STATUS;
}
-
- buffer->Uid = treeCon->ses->Suid; /* always in LE format */
+ /* Uid is not converted */
+ buffer->Uid = treeCon->ses->Suid;
+ buffer->Mid = GetNextMid(treeCon->ses->server);
if(multiuser_mount != 0) {
/* For the multiuser case, there are few obvious technically */
/* possible mechanisms to match the local linux user (uid) */