On Sun, Oct 07, 2018 at 08:16:27PM -0700, David Ahern wrote:
> From: David Ahern <dsah...@gmail.com>
>
> Add a new socket option, NETLINK_DUMP_STRICT_CHK, that userspace
> can use via setsockopt to request strict checking of headers and
> attributes on dump requests.
>
> To get dump features such as kernel side filtering based on data in
> the header or attributes appended to the dump request, userspace
> must call setsockopt() for NETLINK_DUMP_STRICT_CHK and a non-zero
> value. Since the netlink sock and its flags are private to the
> af_netlink code, the strict checking flag is passed to dump handlers
> via a flag in the netlink_callback struct.
>
> For old userspace on new kernel there is no impact as all of the data
> checks in later patches are wrapped in a check on the new strict flag.
>
> For new userspace on old kernel, the setsockopt will fail and even if
> new userspace sets data in the headers and appended attributes the
> kernel will silently ignore it. Moving forward when the setsockopt
> succeeds, the new userspace on old kernel means the dump request can
> pass an attribute the kernel does not understand. The dump will then
> fail as the older kernel does not understand it.
>
> New userspace on new kernel setting the socket option gets the benefit
> of the improved data dump.
>
> Kernel side the NETLINK_DUMP_STRICT_CHK uapi is converted to a generic
> NETLINK_F_STRICT_CHK flag which can potentially be leveraged for tighter
> checking on the NEW, DEL, and SET commands.
>
> Signed-off-by: David Ahern <dsah...@gmail.com>
Thanks for the bool. :)
Acked-by: Christian Brauner <christ...@brauner.io>
> ---
> include/linux/netlink.h | 1 +
> include/uapi/linux/netlink.h | 1 +
> net/netlink/af_netlink.c | 21 ++++++++++++++++++++-
> net/netlink/af_netlink.h | 1 +
> 4 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index 88c8a2d83eb3..72580f1a72a2 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -179,6 +179,7 @@ struct netlink_callback {
> struct netlink_ext_ack *extack;
> u16 family;
> u16 min_dump_alloc;
> + bool strict_check;
> unsigned int prev_seq, seq;
> long args[6];
> };
> diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
> index 776bc92e9118..486ed1f0c0bc 100644
> --- a/include/uapi/linux/netlink.h
> +++ b/include/uapi/linux/netlink.h
> @@ -155,6 +155,7 @@ enum nlmsgerr_attrs {
> #define NETLINK_LIST_MEMBERSHIPS 9
> #define NETLINK_CAP_ACK 10
> #define NETLINK_EXT_ACK 11
> +#define NETLINK_DUMP_STRICT_CHK 12
>
> struct nl_pktinfo {
> __u32 group;
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 7ac585f33a9e..e613a9f89600 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -1706,6 +1706,13 @@ static int netlink_setsockopt(struct socket *sock, int
> level, int optname,
> nlk->flags &= ~NETLINK_F_EXT_ACK;
> err = 0;
> break;
> + case NETLINK_DUMP_STRICT_CHK:
> + if (val)
> + nlk->flags |= NETLINK_F_STRICT_CHK;
> + else
> + nlk->flags &= ~NETLINK_F_STRICT_CHK;
> + err = 0;
> + break;
> default:
> err = -ENOPROTOOPT;
> }
> @@ -1799,6 +1806,15 @@ static int netlink_getsockopt(struct socket *sock, int
> level, int optname,
> return -EFAULT;
> err = 0;
> break;
> + case NETLINK_DUMP_STRICT_CHK:
> + if (len < sizeof(int))
> + return -EINVAL;
> + len = sizeof(int);
> + val = nlk->flags & NETLINK_F_STRICT_CHK ? 1 : 0;
> + if (put_user(len, optlen) || put_user(val, optval))
> + return -EFAULT;
> + err = 0;
> + break;
> default:
> err = -ENOPROTOOPT;
> }
> @@ -2282,9 +2298,9 @@ int __netlink_dump_start(struct sock *ssk, struct
> sk_buff *skb,
> const struct nlmsghdr *nlh,
> struct netlink_dump_control *control)
> {
> + struct netlink_sock *nlk, *nlk2;
> struct netlink_callback *cb;
> struct sock *sk;
> - struct netlink_sock *nlk;
> int ret;
>
> refcount_inc(&skb->users);
> @@ -2318,6 +2334,9 @@ int __netlink_dump_start(struct sock *ssk, struct
> sk_buff *skb,
> cb->min_dump_alloc = control->min_dump_alloc;
> cb->skb = skb;
>
> + nlk2 = nlk_sk(NETLINK_CB(skb).sk);
> + cb->strict_check = !!(nlk2->flags & NETLINK_F_STRICT_CHK);
> +
> if (control->start) {
> ret = control->start(cb);
> if (ret)
> diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
> index 962de7b3c023..5f454c8de6a4 100644
> --- a/net/netlink/af_netlink.h
> +++ b/net/netlink/af_netlink.h
> @@ -15,6 +15,7 @@
> #define NETLINK_F_LISTEN_ALL_NSID 0x10
> #define NETLINK_F_CAP_ACK 0x20
> #define NETLINK_F_EXT_ACK 0x40
> +#define NETLINK_F_STRICT_CHK 0x80
>
> #define NLGRPSZ(x) (ALIGN(x, sizeof(unsigned long) * 8) / 8)
> #define NLGRPLONGS(x) (NLGRPSZ(x)/sizeof(unsigned long))
> --
> 2.11.0
>
