From: Willem de Bruijn <will...@google.com> 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+3joekicrrtevcpxgw4xoc...@mail.gmail.com> Fixes: 1f8b977ab32d ("sock: enable MSG_ZEROCOPY") Reported-by: Andreas Hartmann <andihartm...@01019freenet.de> Reported-by: David Hill <dh...@redhat.com> Signed-off-by: Willem de Bruijn <will...@google.com> --- This fix causes skb_zerocopy_clone to be called for each frag in the array. I will follow-up with a patch to net-next that will call both skb_orphan_frags and skb_zerocopy_clone once per skb only. --- net/core/skbuff.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a592ca025fc4..edf40ac0cd07 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -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); -- 2.15.1.620.gb9897f4670-goog
