linux-kernel - [PATCH 4.14 114/146] skbuff: orphan frags before zerocopy clone

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Date:   Mon,  1 Jan 2018 15:38:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Andreas Hartmann <andihartmann@...19freenet.de>,
        David Hill <dhill@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.14 114/146] skbuff: orphan frags before zerocopy clone

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@...gle.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@...l.gmail.com>
Fixes: 1f8b977ab32d ("sock: enable MSG_ZEROCOPY")
Reported-by: Andreas Hartmann <andihartmann@...19freenet.de>
Reported-by: David Hill <dhill@...hat.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);