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Commit 1853c949 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
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netlink, mmap: transform mmap skb into full skb on taps 

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: bcbde0d4 ("net: netlink: virtual tap device management")
Reported-by: default avatarKen-ichirou MATSUZAWA <chamaken@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Tested-by: default avatarKen-ichirou MATSUZAWA <chamaken@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 64d1def7

net/netlink/af_netlink.c

+23 −7
Original line number Diff line number Diff line
@@ -125,6 +125,24 @@ static inline u32 netlink_group_mask(u32 group) 
	return group ? 1 << (group - 1) : 0;

}



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))
@@ -206,6 +224,10 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb, 
	int ret = -ENOMEM;



	dev_hold(dev);



	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;
@@ -279,11 +301,6 @@ 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;
@@ -846,7 +863,6 @@ 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

net/netlink/af_netlink.h

+9 −0
Original line number Diff line number Diff line
@@ -59,6 +59,15 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk) 
	return container_of(sk, struct netlink_sock, sk);

}



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 rhashtable	hash;

	struct hlist_head	mc_list;