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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.1 006/122] net: test nouarg before dereferencing zerocopy pointers
Date:   Thu, 23 May 2019 21:05:28 +0200
Message-Id: <20190523181705.892932071@linuxfoundation.org>
In-Reply-To: <20190523181705.091418060@linuxfoundation.org>
References: <20190523181705.091418060@linuxfoundation.org>
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From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 185ce5c38ea76f29b6bd9c7c8c7a5e5408834920 ]

Zerocopy skbs without completion notification were added for packet
sockets with PACKET_TX_RING user buffers. Those signal completion
through the TP_STATUS_USER bit in the ring. Zerocopy annotation was
added only to avoid premature notification after clone or orphan, by
triggering a copy on these paths for these packets.

The mechanism had to define a special "no-uarg" mode because packet
sockets already use skb_uarg(skb) == skb_shinfo(skb)->destructor_arg
for a different pointer.

Before deferencing skb_uarg(skb), verify that it is a real pointer.

Fixes: 5cd8d46ea1562 ("packet: copy user buffers before orphan or clone")
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>
---
 include/linux/skbuff.h |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1425,10 +1425,12 @@ static inline void skb_zcopy_clear(struc
 	struct ubuf_info *uarg = skb_zcopy(skb);
 
 	if (uarg) {
-		if (uarg->callback == sock_zerocopy_callback) {
+		if (skb_zcopy_is_nouarg(skb)) {
+			/* no notification callback */
+		} else if (uarg->callback == sock_zerocopy_callback) {
 			uarg->zerocopy = uarg->zerocopy && zerocopy;
 			sock_zerocopy_put(uarg);
-		} else if (!skb_zcopy_is_nouarg(skb)) {
+		} else {
 			uarg->callback(uarg, zerocopy);
 		}
 
@@ -2683,7 +2685,8 @@ static inline int skb_orphan_frags(struc
 {
 	if (likely(!skb_zcopy(skb)))
 		return 0;
-	if (skb_uarg(skb)->callback == sock_zerocopy_callback)
+	if (!skb_zcopy_is_nouarg(skb) &&
+	    skb_uarg(skb)->callback == sock_zerocopy_callback)
 		return 0;
 	return skb_copy_ubufs(skb, gfp_mask);
 }