mnt: Fail collect_mounts when applied to unmounted mounts

The only users of collect_mounts are in audit_tree.c

In audit_trim_trees and audit_add_tree_rule the path passed into
collect_mounts is generated from kern_path passed an audit_tree
pathname which is guaranteed to be an absolute path.   In those cases
collect_mounts is obviously intended to work on mounted paths and
if a race results in paths that are unmounted when collect_mounts
it is reasonable to fail early.

The paths passed into audit_tag_tree don't have the absolute path
check.  But are used to play with fsnotify and otherwise interact with
the audit_trees, so again operating only on mounted paths appears
reasonable.

Avoid having to worry about what happens when we try and audit
unmounted filesystems by restricting collect_mounts to mounts
that appear in the mount tree.

Change-Id: I2edfee6d6951a2179ce8f53785b65ddb1eb95629
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 900812f..8b34a97 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1477,8 +1477,14 @@ struct vfsmount *collect_mounts(struct path *path)
 {
 	struct vfsmount *tree;
 	down_write(&namespace_sem);
-	tree = copy_tree(path->mnt, path->dentry, CL_COPY_ALL | CL_PRIVATE);
+	if (!check_mnt(path->mnt))
+		tree = ERR_PTR(-EINVAL);
+	else
+		tree = copy_tree(path->mnt, path->dentry,
+				 CL_COPY_ALL | CL_PRIVATE);
 	up_write(&namespace_sem);
+	if (IS_ERR(tree))
+		return NULL;
 	return tree;
 }