Patch "skbuff: orphan frags before zerocopy clone" has been added to the 4.14-stable tree

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;a=summary

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 <[email protected]> know about it.

From: Willem de Bruijn <[email protected]>
Date: Wed, 20 Dec 2017 17:37:49 -0500
Subject: skbuff: orphan frags before zerocopy clone

From: Willem de Bruijn <[email protected]>

[ 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.

---
 net/core/skbuff.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -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 [email protected] 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