msdfs on 3.0.25b - trailing backslash problem; parent dir content showing up in a subdir

[Jan Martin]

Note: This is the first one of three similar msdfs problems. To avoid
confusion, we call this one the "trailing backslash problem"


Hi all,

in rare cases, Samba 3.0.25b shows directory contents at the wrong
position in the file tree when displaying a subdirectory of a DFS link.

The problem occurs whenever Windows XP asks for a DFS referral for a
subdirectory of a DFS link with a trailing backslash.
Windows does not do this very often, but we saw it several times per day
on our central DFS server.

smbd/msdfs.c, dfs_path_lookup() does the following with the requested
path:
- in line 390, the local copy 'localpath' is 'unix_convert'ed; the
trailing backslash is removed inside unix_convert
- in lines 417-20, 'dfspath' (another copy of the requested path) is
mangled another way without removing trailing backslashes

That's why the following loop (lines 435-461) that is meant to
synchronously cut off the last path component from both strings until it
comes to a DFS link, does not handle both strings the same.  When the
original path ended with a backslash, 'canon_dfspath' has always one
component more than 'localpath', so that *consumedcntp gets too big in
line 446. This value is reported to the client.

Upon that answer, the clients composes the DFS destination, omitting the
'consumed' part of the original UNC name.
Example:
Original UNC name: \\DFSSERVER\DFSROOT\DFSLINK\SUBDIR\
Answer from DFSSERVER: "Look at \\REALSERVER\REALSHARE; but
\DFSROOT\DFSLINK\SUBDIR\ is already consumed"
So the client shows \\REALSERVER\REALSHARE instead of
\\REALSERVER\REALSHARE\SUBDIR as content of
\\DFSSERVER\DFSROOT\DFSLINK\SUBDIR

To fix that problem, we added a line to trim canon_dfspath in
smbd/msdfs.c, line 430.
This is our patch (4 lines comment, 1 line code):
-------------------------------------------------
diff -rU5 samba-3.0.25b-orig/source/smbd/msdfs.c
samba-3.0.25b-backslash-fix/source/smbd/msdfs.c
--- samba-3.0.25b-orig/source/smbd/msdfs.c      2007-05-11
00:09:34.000000000 +0200
+++ samba-3.0.25b-backslash-fix/source/smbd/msdfs.c     2007-08-06
14:58:41.000000000 +0200
@@ -425,10 +425,16 @@
         * local path, chopping off the last component
         * in both the local path and the canonicalized
         * DFS path. If we hit a DFS link then we're done.
         */
 
+        /* localpath comes out of unix_convert, so it has
+         * no trailing backslash
+         * make sure that canon_dfspath hasn't either
+         */
+        trim_char(canon_dfspath,0,'/');
+
        p = strrchr_m(localpath, '/');
        if (consumedcntp) {
                q = strrchr_m(canon_dfspath, '/');
        }

-------------------------------------------------

With this patch, our installation does not show the problem any more.
Would you please check and add it (or a better one, of course) to the
Samba sources?

Thank you very much in advance

And again - we will publish two different problems here soon, along with
solution proposals; please don't get confused. This is the trailing
backslash problem.


Jan Martin