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Commit 268b7906 authored by Willem de Bruijn's avatar Willem de Bruijn Committed by David S. Miller
Browse files

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: default avatarAndreas Hartmann <andihartmann@01019freenet.de>
Reported-by: default avatarDavid Hill <dhill@redhat.com>
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarDavid 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 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, 


		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 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, 


			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);