[PATCH 4.14 62/62] libceph: fall back to sendmsg for slab pages

Greg Kroah-Hartman
2018-11-26T11:01:24Z

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;