Commit 268b7906 authored Dec 20, 2017 by Willem de Bruijn Committed by David S. Miller Dec 21, 2017

skbuff: orphan frags before zerocopy clone

Call skb_zerocopy_clone after skb_orphan_frags, to avoid duplicate
calls to skb_uarg(skb)->callback for the same data.

skb_zerocopy_clone associates skb_shinfo(skb)->uarg from frag_skb
with each segment. This is only safe for uargs that do refcounting,
which is those that pass skb_orphan_frags without dropping their
shared frags. For others, skb_orphan_frags drops the user frags and
sets the uarg to NULL, after which sock_zerocopy_clone has no effect.

Qemu hangs were reported due to duplicate vhost_net_zerocopy_callback
calls for the same data causing the vhost_net_ubuf_ref_>refcount to
drop below zero.

Link: http://lkml.kernel.org/r/<CAF=yD-LWyCD4Y0aJ9O0e_CHLR+3JOeKicRRTEVCPxgw4XOcqGQ@mail.gmail.com

>
Fixes: 1f8b977a ("sock: enable MSG_ZEROCOPY")
Reported-by: Andreas Hartmann <andihartmann@01019freenet.de>
Reported-by: David Hill <dhill@redhat.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 513674b5

net/core/skbuff.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -3654,8 +3654,6 @@ normal:

		skb_shinfo(nskb)->tx_flags \|= skb_shinfo(head_skb)->tx_flags &
		SKBTX_SHARED_FRAG;
		if (skb_zerocopy_clone(nskb, head_skb, GFP_ATOMIC))
		goto err;

		while (pos < offset + len) {
		if (i >= nfrags) {
		@@ -3681,6 +3679,8 @@ normal:

		if (unlikely(skb_orphan_frags(frag_skb, GFP_ATOMIC)))
		goto err;
		if (skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC))
		goto err;

		nskb_frag = frag;
		__skb_frag_ref(nskb_frag);

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