Commit 1f282cdc authored by Al Viro's avatar Al Viro
Browse files

fs/fhandle.c: fix a race in call of has_locked_children() 



may_decode_fh() is calling has_locked_children() while holding no locks.
That's an oopsable race...

The rest of the callers are safe since they are holding namespace_sem and
are guaranteed a positive refcount on the mount in question.

Rename the current has_locked_children() to __has_locked_children(), make
it static and switch the fs/namespace.c users to it.

Make has_locked_children() a wrapper for __has_locked_children(), calling
the latter under read_seqlock_excl(&mount_lock).

Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Fixes: 620c266f ("fhandle: relax open_by_handle_at() permission checks")
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent a82ba839

fs/namespace.c

+14 −4
Original line number Diff line number Diff line
@@ -2425,7 +2425,7 @@ void drop_collected_mounts(struct vfsmount *mnt) 
	namespace_unlock();

}



bool has_locked_children(struct mount *mnt, struct dentry *dentry)

static bool __has_locked_children(struct mount *mnt, struct dentry *dentry)

{

	struct mount *child;
@@ -2439,6 +2439,16 @@ bool has_locked_children(struct mount *mnt, struct dentry *dentry) 
	return false;

}



bool has_locked_children(struct mount *mnt, struct dentry *dentry)

{

	bool res;



	read_seqlock_excl(&mount_lock);

	res = __has_locked_children(mnt, dentry);

	read_sequnlock_excl(&mount_lock);

	return res;

}



/*

 * Check that there aren't references to earlier/same mount namespaces in the

 * specified subtree.  Such references can act as pins for mount namespaces
@@ -2499,7 +2509,7 @@ struct vfsmount *clone_private_mount(const struct path *path) 
			return ERR_PTR(-EINVAL);

	}



	if (has_locked_children(old_mnt, path->dentry))

	if (__has_locked_children(old_mnt, path->dentry))

		return ERR_PTR(-EINVAL);



	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
@@ -3036,7 +3046,7 @@ static struct mount *__do_loopback(struct path *old_path, int recurse) 
	if (!may_copy_tree(old_path))

		return mnt;



	if (!recurse && has_locked_children(old, old_path->dentry))

	if (!recurse && __has_locked_children(old, old_path->dentry))

		return mnt;



	if (recurse)
@@ -3429,7 +3439,7 @@ static int do_set_group(struct path *from_path, struct path *to_path) 
		goto out;



	/* From mount should not have locked children in place of To's root */

	if (has_locked_children(from, to->mnt.mnt_root))

	if (__has_locked_children(from, to->mnt.mnt_root))

		goto out;



	/* Setting sharing groups is only allowed on private mounts */