Commit 550f7ca9 authored by Max Kellermann's avatar Max Kellermann Committed by Ilya Dryomov
Browse files

ceph: give up on paths longer than PATH_MAX 



If the full path to be built by ceph_mdsc_build_path() happens to be
longer than PATH_MAX, then this function will enter an endless (retry)
loop, effectively blocking the whole task.  Most of the machine
becomes unusable, making this a very simple and effective DoS
vulnerability.

I cannot imagine why this retry was ever implemented, but it seems
rather useless and harmful to me.  Let's remove it and fail with
ENAMETOOLONG instead.

Cc: stable@vger.kernel.org
Reported-by: default avatarDario Weißer <dario@cure53.de>
Signed-off-by: default avatarMax Kellermann <max.kellermann@ionos.com>
Reviewed-by: default avatarAlex Markuze <amarkuze@redhat.com>
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
parent d6fd6f82

fs/ceph/mds_client.c

+4 −5
Original line number Diff line number Diff line
@@ -2800,12 +2800,11 @@ char *ceph_mdsc_build_path(struct ceph_mds_client *mdsc, struct dentry *dentry, 


	if (pos < 0) {

		/*

		 * A rename didn't occur, but somehow we didn't end up where

		 * we thought we would. Throw a warning and try again.

		 * The path is longer than PATH_MAX and this function

		 * cannot ever succeed.  Creating paths that long is

		 * possible with Ceph, but Linux cannot use them.

		 */

		pr_warn_client(cl, "did not end path lookup where expected (pos = %d)\n",

			       pos);

		goto retry;

		return ERR_PTR(-ENAMETOOLONG);

	}



	*pbase = base;