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Subject[PATCH 3.16.y-ckt 129/133] netlink, mmap: transform mmap skb into full skb on taps
Date
3.16.7-ckt18 -stable review patch.  If anyone has any objections, please let me know.

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

From: Daniel Borkmann <daniel@iogearbox.net>

commit 1853c949646005b5959c483becde86608f548f24 upstream.

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
Fixes: bcbde0d449ed ("net: netlink: virtual tap device management")
Reported-by: Ken-ichirou MATSUZAWA <chamaken@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Ken-ichirou MATSUZAWA <chamaken@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
net/netlink/af_netlink.c | 30 +++++++++++++++++++++++-------
net/netlink/af_netlink.h | 9 +++++++++
2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 329f48404fa0..5f5c976b369d 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -115,6 +115,24 @@ static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u
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(struct sk_buff *skb,
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 *sk)
}

#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(struct sock *sk, struct sk_buff *skb)
}

#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
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d441f5b6..4b0a5eb0c6b4 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -67,6 +67,15 @@ 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;

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