4.1-stable review patch. If anyone has any objections, please let me know.
------------------ From: Daniel Borkmann <dan...@iogearbox.net> [ 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 Fixes: bcbde0d449ed ("net: netlink: virtual tap device management") Reported-by: Ken-ichirou MATSUZAWA <chama...@gmail.com> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net> Tested-by: Ken-ichirou MATSUZAWA <chama...@gmail.com> Signed-off-by: David S. Miller <da...@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- net/netlink/af_netlink.c | 30 +++++++++++++++++++++++------- net/netlink/af_netlink.h | 9 +++++++++ 2 files changed, 32 insertions(+), 7 deletions(-) --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -123,6 +123,24 @@ static inline u32 netlink_group_mask(u32 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)) @@ -204,7 +222,11 @@ 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); @@ -276,11 +298,6 @@ 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; @@ -832,7 +849,6 @@ 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 --- a/net/netlink/af_netlink.h +++ b/net/netlink/af_netlink.h @@ -59,6 +59,15 @@ static inline struct netlink_sock *nlk_s 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
