4.14-stable review patch. If anyone has any objections, please let me know.
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From: Ilya Dryomov idryomov@gmail.com
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: Ilya Dryomov idryomov@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/ceph/messenger.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/net/ceph/messenger.c +++ b/net/ceph/messenger.c @@ -594,9 +594,15 @@ static int ceph_tcp_sendpage(struct sock struct bio_vec bvec; int ret;
- /* sendpage cannot properly handle pages with page_count == 0, - * we need to fallback to sendmsg if that's the case */ - if (page_count(page) >= 1) + /* + * sendpage cannot properly handle pages with page_count == 0, + * we need to fall back to sendmsg if that's the case. + * + * Same goes for slab pages: skb_can_coalesce() allows + * coalescing neighboring slab objects into a single frag which + * triggers one of hardened usercopy checks. + */ + if (page_count(page) >= 1 && !PageSlab(page)) return __ceph_tcp_sendpage(sock, page, offset, size, more);
bvec.bv_page = page;