[linux-cifs-client] [PATCH] cifs: fix regression in DFS referral option parsing code

[Jeff Layton]

I believe this patch:

    commit 2c55608f28444c3f33b10312881384c470ceed56
    Author: Igor Mammedov <niallain at gmail.com>
    Date:   Thu Oct 23 13:58:42 2008 +0400

        Fixed parsing of mount options when doing DFS submount

...has caused a regression in the DFS referral handling code. I have the
following mounted:

//hostname/dfsroot

...in this DFS root, I have a dfs referral link that points to:

msdfs:hostname.foo.bar\export

...when I try to traverse this link, compose_mount_options attaches a
prefixpath to the options, even though one shouldn't be there. The
problem is that strlen(fullpath) is != to ref->path_consumed in this
situation so we end up trying to build a prefixpath out of nothing.

I'm not convinced here that trying to work with path_consumed is at all
correct. Why shouldn't we just try to walk the string starting after the
sharename and use whatever is there as the prefixpath? The following
patch seems simpler to me and seems to fix the regressions I've seen in
my setup.

Is there some reason we need to use the more complex scheme that was
introduced by the patch above?

Long term, I think we need to consider adding some generic functions
to do UNC parsing. That would be helpful in the standard cifs_mount
codepath as well and would allow us to make a robust function that
can handle different UNC variations.

Signed-off-by: Jeff Layton <jlayton at redhat.com>
---
 fs/cifs/cifs_dfs_ref.c |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index e1c1836..aa4feef 100644
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -128,7 +128,6 @@ static char *compose_mount_options(const char *sb_mountdata,
 	char *srvIP = NULL;
 	char sep = ',';
 	int off, noff;
-	char *fullpath;
 
 	if (sb_mountdata == NULL)
 		return ERR_PTR(-EINVAL);
@@ -200,16 +199,13 @@ static char *compose_mount_options(const char *sb_mountdata,
 	if (tkn_e == NULL) /* invalid unc, missing share name*/
 		goto compose_mount_options_out;
 
-	fullpath = build_path_from_dentry(dentry);
 	tkn_e = strchr(tkn_e + 1, '\\');
-	if (tkn_e || strlen(fullpath) - (ref->path_consumed)) {
+	if (tkn_e) {
 		strncat(mountdata, &sep, 1);
 		strcat(mountdata, "prefixpath=");
 		if (tkn_e)
 			strcat(mountdata, tkn_e + 1);
-		strcat(mountdata, fullpath + (ref->path_consumed));
 	}
-	kfree(fullpath);
 
 	/*cFYI(1,("%s: parent mountdata: %s", __func__,sb_mountdata));*/
 	/*cFYI(1, ("%s: submount mountdata: %s", __func__, mountdata ));*/
-- 
1.5.5.1