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libceph: fall back to sendmsg for slab pages

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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>
This commit is contained in:
Ilya Dryomov 2018-11-08 15:55:37 +01:00
parent 9ff01193a2
commit 7e241f647d
1 changed files with 9 additions and 3 deletions
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12
net/ceph/messenger.c
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@ -580,9 +580,15 @@ static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
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;