This is a note to let you know that I've just added the patch titled

skbuff: orphan frags before zerocopy clone

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: skbuff-orphan-frags-before-zerocopy-clone.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Dec 31 11:12:48 CET 2017

From: Willem de Bruijn willemb@google.com Date: Wed, 20 Dec 2017 17:37:49 -0500 Subject: skbuff: orphan frags before zerocopy clone

From: Willem de Bruijn willemb@google.com

[ Upstream commit 268b790679422a89e9ab0685d9f291edae780c98 ]

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: 1f8b977ab32d ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/skbuff.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3657,8 +3657,6 @@ 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) { @@ -3684,6 +3682,8 @@ 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);

Patches currently in stable-queue which might be from willemb@google.com are

queue-4.14/skbuff-skb_copy_ubufs-must-release-uarg-even-without-user-frags.patch queue-4.14/sock-free-skb-in-skb_complete_tx_timestamp-on-error.patch queue-4.14/skbuff-orphan-frags-before-zerocopy-clone.patch queue-4.14/skbuff-in-skb_copy_ubufs-unclone-before-releasing-zerocopy.patch