[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, 36 insertions, 12 deletions

diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index e1c18362ba4..85c0a74d034 100644
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -122,7 +122,7 @@ static char *compose_mount_options(const char *sb_mountdata,
                                    char **devname)
 {
         int rc;
-        char *mountdata;
+        char *mountdata = NULL;
         int md_len;
         char *tkn_e;
         char *srvIP = NULL;
@@ -136,10 +136,9 @@ static char *compose_mount_options(const char *sb_mountdata,
         *devname = cifs_get_share_name(ref->node_name);
         rc = dns_resolve_server_name_to_ip(*devname, &srvIP);
         if (rc != 0) {
-                cERROR(1, ("%s: Failed to resolve server part of %s to IP",
-                          __func__, *devname));
-                mountdata = ERR_PTR(rc);
-                goto compose_mount_options_out;
+                cERROR(1, ("%s: Failed to resolve server part of %s to IP: %d",
+                          __func__, *devname, rc));;
+                goto compose_mount_options_err;
         }
         /* md_len = strlen(...) + 12 for 'sep+prefixpath='
          * assuming that we have 'unc=' and 'ip=' in
@@ -149,8 +148,8 @@ static char *compose_mount_options(const char *sb_mountdata,
                 strlen(ref->node_name) + 12;
         mountdata = kzalloc(md_len+1, GFP_KERNEL);
         if (mountdata == NULL) {
-                mountdata = ERR_PTR(-ENOMEM);
-                goto compose_mount_options_out;
+                rc = -ENOMEM;
+                goto compose_mount_options_err;
         }
 
         /* copy all options except of unc,ip,prefixpath */
@@ -197,18 +196,32 @@ static char *compose_mount_options(const char *sb_mountdata,
 
         /* find & copy prefixpath */
         tkn_e = strchr(ref->node_name + 2, '\\');
-        if (tkn_e == NULL) /* invalid unc, missing share name*/
-                goto compose_mount_options_out;
+        if (tkn_e == NULL) {
+                /* invalid unc, missing share name*/
+                rc = -EINVAL;
+                goto compose_mount_options_err;
+        }
 
+        /*
+         * this function gives us a path with a double backslash prefix. We
+         * require a single backslash for DFS. Temporarily increment fullpath
+         * to put it in the proper form and decrement before freeing it.
+         */
         fullpath = build_path_from_dentry(dentry);
+        if (!fullpath) {
+                rc = -ENOMEM;
+                goto compose_mount_options_err;
+        }
+        ++fullpath;
         tkn_e = strchr(tkn_e + 1, '\\');
-        if (tkn_e || strlen(fullpath) - (ref->path_consumed)) {
+        if (tkn_e || (strlen(fullpath) - ref->path_consumed)) {
                 strncat(mountdata, &sep, 1);
                 strcat(mountdata, "prefixpath=");
                 if (tkn_e)
                         strcat(mountdata, tkn_e + 1);
-                strcat(mountdata, fullpath + (ref->path_consumed));
+                strcat(mountdata, fullpath + ref->path_consumed);
         }
+        --fullpath;
         kfree(fullpath);
 
         /*cFYI(1,("%s: parent mountdata: %s", __func__,sb_mountdata));*/
@@ -217,6 +230,11 @@ static char *compose_mount_options(const char *sb_mountdata,
 compose_mount_options_out:
         kfree(srvIP);
         return mountdata;
+
+compose_mount_options_err:
+        kfree(mountdata);
+        mountdata = ERR_PTR(rc);
+        goto compose_mount_options_out;
 }
 
 
@@ -309,13 +327,19 @@ cifs_dfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
                 goto out_err;
         }
 
+        /*
+         * The MSDFS spec states that paths in DFS referral requests and
+         * responses must be prefixed by a single '\' character instead of
+         * the double backslashes usually used in the UNC. This function
+         * gives us the latter, so we must adjust the result.
+         */
         full_path = build_path_from_dentry(dentry);
         if (full_path == NULL) {
                 rc = -ENOMEM;
                 goto out_err;
         }
 
-        rc = get_dfs_path(xid, ses , full_path, cifs_sb->local_nls,
+        rc = get_dfs_path(xid, ses , full_path + 1, cifs_sb->local_nls,
                 &num_referrals, &referrals,
                 cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);