orangefs: keep the readdir entry size 64-bit in fill_from_part()

orangefs: keep the readdir entry size 64-bit in fill_from_part()

fill_from_part() computes the size of a directory entry in size_t but
stores it in a __u32. An entry length near U32_MAX wraps it to a small
value, bypasses the bounds check, and is then used to index the entry,
reading far past the directory part -- an out-of-bounds read that oopses
the kernel.

Compute the size as a u64 so it cannot truncate; the bounds check then
rejects the entry. The trailer is supplied by the userspace client.

Fixes: 480e3e532e31 ("orangefs: support very large directories")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260619-b4-disp-50d2bd59-v1-1-ce332969b4a2@proton.me
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>