[PATCH 4.4 25/25] ovl: prevent private clone if bind mount is not allowed

Greg Kroah-Hartman
2021-08-13T15:09:47Z

From: Miklos Szeredi <mszeredi@redhat.com>

commit 427215d85e8d1476da1a86b8d67aceb485eb3631 upstream.

Add the following checks from __do_loopback() to clone_private_mount() as
well:

- verify that the mount is in the current namespace

- verify that there are no locked children

Reported-by: Alois Wohlschlager <alois1@gmx-topmail.de>
Fixes: c771d683a62e ("vfs: introduce clone_private_mount()")
Cc: <stable@vger.kernel.org> # v3.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/namespace.c | 42 +++++++++++++++++++++++++++---------------
1 file changed, 27 insertions(+), 15 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1830,6 +1830,20 @@ void drop_collected_mounts(struct vfsmou
namespace_unlock();
}

+static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
+{
+ struct mount *child;
+
+ list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+ if (!is_subdir(child->mnt_mountpoint, dentry))
+ continue;
+
+ if (child->mnt.mnt_flags & MNT_LOCKED)
+ return true;
+ }
+ return false;
+}
+
/**
* clone_private_mount - create a private clone of a path
*
@@ -1844,16 +1858,27 @@ struct vfsmount *clone_private_mount(str
struct mount *old_mnt = real_mount(path->mnt);
struct mount *new_mnt;

+ down_read(&namespace_sem);
if (IS_MNT_UNBINDABLE(old_mnt))
- return ERR_PTR(-EINVAL);
+ goto invalid;
+
+ if (!check_mnt(old_mnt))
+ goto invalid;
+
+ if (has_locked_children(old_mnt, path->dentry))
+ goto invalid;

- down_read(&namespace_sem);
new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
up_read(&namespace_sem);
+
if (IS_ERR(new_mnt))
return ERR_CAST(new_mnt);

return &new_mnt->mnt;
+
+invalid:
+ up_read(&namespace_sem);
+ return ERR_PTR(-EINVAL);
}
EXPORT_SYMBOL_GPL(clone_private_mount);

@@ -2169,19 +2194,6 @@ static int do_change_type(struct path *p
return err;
}

-static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
-{
- struct mount *child;
- list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
- if (!is_subdir(child->mnt_mountpoint, dentry))
- continue;
-
- if (child->mnt.mnt_flags & MNT_LOCKED)
- return true;
- }
- return false;
-}
-
/*
* do loopback mount.
*/