cifs: fix error handling in mount-time DFS referral chasing code

If the referral is malformed or the hostname can't be resolved, then
the current code generates an oops. Fix it to handle these errors
gracefully.

Reported-by: Sandro Mathys <sm@sandro-mathys.ch>
Acked-by: Igor Mammedov <niallain@gmail.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifs_dfs_ref.c

@@ -55,7 +55,7 @@ void cifs_dfs_release_automount_timer(void)
  * i.e. strips from UNC trailing path that is not part of share
  * name and fixup missing '\' in the begining of DFS node refferal
  * if neccessary.
- * Returns pointer to share name on success or NULL on error.
+ * Returns pointer to share name on success or ERR_PTR on error.
  * Caller is responsible for freeing returned string.
  */
 static char *cifs_get_share_name(const char *node_name)
@@ -68,7 +68,7 @@ static char *cifs_get_share_name(const char *node_name)
 	UNC = kmalloc(len+2 /*for term null and additional \ if it's missed */,
 			 GFP_KERNEL);
 	if (!UNC)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	/* get share name and server name */
 	if (node_name[1] != '\\') {
@@ -87,7 +87,7 @@ static char *cifs_get_share_name(const char *node_name)
 		cERROR(1, ("%s: no server name end in node name: %s",
 			__func__, node_name));
 		kfree(UNC);
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	/* find sharename end */
@@ -133,6 +133,12 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
 		return ERR_PTR(-EINVAL);
 
 	*devname = cifs_get_share_name(ref->node_name);
+	if (IS_ERR(*devname)) {
+		rc = PTR_ERR(*devname);
+		*devname = NULL;
+		goto compose_mount_options_err;
+	}
+
 	rc = dns_resolve_server_name_to_ip(*devname, &srvIP);
 	if (rc != 0) {
 		cERROR(1, ("%s: Failed to resolve server part of %s to IP: %d",

fs/cifs/connect.c

@@ -2544,20 +2544,27 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 
 			if (mount_data != mount_data_global)
 				kfree(mount_data);
+
 			mount_data = cifs_compose_mount_options(
 					cifs_sb->mountdata, full_path + 1,
 					referrals, &fake_devname);
-			kfree(fake_devname);
+
 			free_dfs_info_array(referrals, num_referrals);
+			kfree(fake_devname);
+			kfree(full_path);
+
+			if (IS_ERR(mount_data)) {
+				rc = PTR_ERR(mount_data);
+				mount_data = NULL;
+				goto mount_fail_check;
+			}
 
 			if (tcon)
 				cifs_put_tcon(tcon);
 			else if (pSesInfo)
 				cifs_put_smb_ses(pSesInfo);
 
 			cleanup_volume_info(&volume_info);
-			FreeXid(xid);
-			kfree(full_path);
 			referral_walks_count++;
 			goto try_mount_again;
 		}