From 550f7ca98ee028a606aa75705a7e77b1bd11720f Mon Sep 17 00:00:00 2001 From: Max Kellermann Date: Mon, 18 Nov 2024 23:28:28 +0100 Subject: [PATCH] ceph: give up on paths longer than PATH_MAX MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Dario Weißer Signed-off-by: Max Kellermann Reviewed-by: Alex Markuze Signed-off-by: Ilya Dryomov --- fs/ceph/mds_client.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index 219a2cc2bf3c..785fe489ef4b 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -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;