On Fri, 2015-07-10 at 14:51 +0300, Konstantin Khlebnikov wrote:
> This fixes race between non-atomic updates of adjacent bit-fields:
> skb->cloned could be lost because netlink broadcast clones skb after
> sending it to the first listener who sets skb->peeked at the same skb.
> As a result atomic refcounting of skb header stays disabled and
> skb_release_data() frees it twice. Race leads to double-free in kmalloc-xxx.
>
> Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
> Fixes: b19372273164 ("net: reorganize sk_buff for faster __copy_skb_header()")
> ---
> net/netlink/af_netlink.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index dea925388a5b..921e0d8dfe3a 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -2028,6 +2028,12 @@ int netlink_broadcast_filtered(struct sock *ssk,
> struct sk_buff *skb, u32 portid
> info.tx_filter = filter;
> info.tx_data = filter_data;
>
> + /* Enable atomic refcounting in skb_release_data() before first send:
> + * non-atomic set of that bit-field in __skb_clone() could race with
> + * __skb_recv_datagram() which touches the same set of bit-fields.
> + */
> + skb->cloned = 1;
> +
> /* While we sleep in clone, do not allow to change socket list */
>
> netlink_lock_table();
Wow, this is tricky.
I wonder how you found this bug ????
Acked-by: Eric Dumazet <eduma...@google.com>
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