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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: bcbde0d449 ("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>
This commit is contained in:
Daniel Borkmann 2015-09-10 20:05:46 +02:00 committed by David S. Miller
parent 64d1def7d3
commit 1853c94964
2 changed files with 32 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
net/netlink/af_netlink.c
View File

@ -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))
@ -206,7 +224,11 @@ 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);
@ -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

9
net/netlink/af_netlink.h
View File

@ -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;