From: Max Kellermann max.kellermann@ionos.com
commit 550f7ca98ee028a606aa75705a7e77b1bd11720f upstream.
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 dario@cure53.de Signed-off-by: Max Kellermann max.kellermann@ionos.com Reviewed-by: Alex Markuze amarkuze@redhat.com Signed-off-by: Ilya Dryomov idryomov@gmail.com [idryomov@gmail.com: backport to 6.1: pr_warn() is still in use] --- 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 da9fcf48ab6c..741ca7d10032 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -2447,12 +2447,11 @@ char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *pbase,
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("build_path did not end path lookup where " - "expected, pos is %d\n", pos); - goto retry; + return ERR_PTR(-ENAMETOOLONG); }
*pbase = base;