Patch "netlink, mmap: transform mmap skb into full skb on taps" has been added to the 3.14-stable tree

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

netlink, mmap: transform mmap skb into full skb on taps

to the 3.14-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:
netlink-mmap-transform-mmap-skb-into-full-skb-on-taps.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Borkmann <[email protected]>
Date: Thu, 10 Sep 2015 20:05:46 +0200
Subject: netlink, mmap: transform mmap skb into full skb on taps

From: Daniel Borkmann <[email protected]>

[ Upstream commit 1853c949646005b5959c483becde86608f548f24 ]

Ken-ichirou reported that running netlink in mmap mode for receive in combination with nlmon will throw a NULL pointer dereference in __kfree_skb() on nlmon_xmit(), in my case I can also trigger an "unable to handle kernel paging request". The problem is the skb_clone() in __netlink_deliver_tap_skb() for skbs that are mmaped.

I.e. the cloned skb doesn't have a destructor, whereas the mmap netlink skb has it pointed to netlink_skb_destructor(), set in the handler netlink_ring_setup_skb(). There, skb->head is being set to NULL, so that in such cases, __kfree_skb() doesn't perform a skb_release_data() via skb_release_all(), where skb->head is possibly being freed through kfree(head) into slab allocator, although netlink mmap skb->head points to the mmap buffer. Similarly, the same has to be done also for large netlink skbs where the data area is vmalloced. Therefore, as discussed, make a copy for these rather rare cases for now. This fixes the issue on my and Ken-ichirou's test-cases.

Reference: http://thread.gmane.org/gmane.linux.network/371129

---
 net/netlink/af_netlink.c |   30 +++++++++++++++++++++++-------
 net/netlink/af_netlink.h |    9 +++++++++
 2 files changed, 32 insertions(+), 7 deletions(-)

@@ -115,6 +115,24 @@ static inline struct hlist_head *nl_port
 	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
 }
 
+static struct sk_buff *netlink_to_full_skb(const struct sk_buff *skb,
+					   gfp_t gfp_mask)
+{
+	unsigned int len = skb_end_offset(skb);
+	struct sk_buff *new;
+
+	new = alloc_skb(len, gfp_mask);
+	if (new == NULL)
+		return NULL;
+
+	NETLINK_CB(new).portid = NETLINK_CB(skb).portid;
+	NETLINK_CB(new).dst_group = NETLINK_CB(skb).dst_group;
+	NETLINK_CB(new).creds = NETLINK_CB(skb).creds;
+
+	memcpy(skb_put(new, len), skb->data, len);
+	return new;
+}
+
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))

@@ -199,7 +217,11 @@ static int __netlink_deliver_tap_skb(str
 	int ret = -ENOMEM;
 
 	dev_hold(dev);
-	nskb = skb_clone(skb, GFP_ATOMIC);
+
+	if (netlink_skb_is_mmaped(skb) || is_vmalloc_addr(skb->head))
+		nskb = netlink_to_full_skb(skb, GFP_ATOMIC);
+	else
+		nskb = skb_clone(skb, GFP_ATOMIC);
 	if (nskb) {
 		nskb->dev = dev;
 		nskb->protocol = htons((u16) sk->sk_protocol);

@@ -271,11 +293,6 @@ static void netlink_rcv_wake(struct sock
 }
 
 #ifdef CONFIG_NETLINK_MMAP
-static bool netlink_skb_is_mmaped(const struct sk_buff *skb)
-{
-	return NETLINK_CB(skb).flags & NETLINK_SKB_MMAPED;
-}
-
 static bool netlink_rx_is_mmaped(struct sock *sk)
 {
 	return nlk_sk(sk)->rx_ring.pg_vec != NULL;

@@ -827,7 +844,6 @@ static void netlink_ring_set_copied(stru
 }
 
 #else /* CONFIG_NETLINK_MMAP */
-#define netlink_skb_is_mmaped(skb)	false
 #define netlink_rx_is_mmaped(sk)	false
 #define netlink_tx_is_mmaped(sk)	false
 #define netlink_mmap			sock_no_mmap

@@ -65,6 +65,15 @@ struct nl_portid_hash {
 	u32			rnd;
 };
 
+static inline bool netlink_skb_is_mmaped(const struct sk_buff *skb)
+{
+#ifdef CONFIG_NETLINK_MMAP
+	return NETLINK_CB(skb).flags & NETLINK_SKB_MMAPED;
+#else
+	return false;
+#endif /* CONFIG_NETLINK_MMAP */
+}
+
 struct netlink_table {
 	struct nl_portid_hash	hash;
 	struct hlist_head	mc_list;

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/ipv6-fix-exthdrs-offload-registration-in-out_rt-path.patch queue-3.14/rtnetlink-verify-ifla_vf_info-attributes-before-passing-them-to-driver.patch queue-3.14/netlink-mmap-transform-mmap-skb-into-full-skb-on-taps.patch