libceph: fall back to sendmsg for slab pages
commit 7e241f647dc7087a0401418a187f3f5b527cc690 upstream. skb_can_coalesce() allows coalescing neighboring slab objects into a single frag: return page == skb_frag_page(frag) && off == frag->page_offset + skb_frag_size(frag); ceph_tcp_sendpage() can be handed slab pages. One example of this is XFS: it passes down sector sized slab objects for its metadata I/O. If the kernel client is co-located on the OSD node, the skb may go through loopback and pop on the receive side with the exact same set of frags. When tcp_recvmsg() attempts to copy out such a frag, hardened usercopy complains because the size exceeds the object's allocated size: usercopy: kernel memory exposure attempt detected from ffff9ba917f20a00 (kmalloc-512) (1024 bytes) Although skb_can_coalesce() could be taught to return false if the resulting frag would cross a slab object boundary, we already have a fallback for non-refcounted pages. Utilize it for slab pages too. Cc: stable@vger.kernel.org # 4.8+ Signed-off-by: NIlya Dryomov <idryomov@gmail.com> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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