[CIFS] make sure that DFS pathnames are properly formed

The paths in a DFS request are supposed to only have a single preceding
backslash, but we are sending them with a double backslash. This is
exposing a bug in Windows where it also sends a path in the response
that has a double backslash.

The existing code that builds the mount option string however expects a
double backslash prefix in a couple of places when it tries to use the
path returned by build_path_from_dentry. Fix compose_mount_options to
expect properly formed DFS paths (single backslash at front).

Also clean up error handling in that function. There was a possible
NULL pointer dereference and situations where a partially built option
string would be returned.

Tested against Samba 3.0.28-ish server and Samba 3.3 and Win2k8.

CC: Stable <stable@kernel.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index 5ab6bcce880a..080703a15f44 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -4,7 +4,8 @@ Add "forcemandatorylock" mount option to allow user to use mandatory
 rather than posix (advisory) byte range locks, even though server would
 support posix byte range locks.  Fix query of root inode when prefixpath
 specified and user does not have access to query information about the
-top of the share.
+top of the share.  Fix problem in 2.6.28 resolving DFS paths to
+Samba servers (worked to Windows).
 
 Version 1.55
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