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@xxxxxxxxxxxxxxx
Reported-by: Dario Weißer <dario@xxxxxxxxx>
Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
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 c4a5fd94bbbb..4f6ac015edcd 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2808,12 +2808,11 @@ 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;
--
2.45.2
