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Date: Wed, 28 Jan 2015 11:40:39 -0500
From: Willem de Bruijn <willemb@...gle.com>
To: Network Development <netdev@...r.kernel.org>
Cc: David Miller <davem@...emloft.net>,
Richard Cochran <richardcochran@...il.com>,
Andy Lutomirski <luto@...capital.net>,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next v1 2/3] net-timestamp: no-payload only sysctl
On Wed, Jan 28, 2015 at 11:28 AM, Willem de Bruijn <willemb@...gle.com> wrote:
> Tx timestamps are looped onto the error queue on top of an skb. This
> mechanism leaks packet headers to processes unless the no-payload
> options SOF_TIMESTAMPING_OPT_TSONLY is set.
>
> Add a sysctl that optionally drops looped timestamp with data. This
> only affects processes without CAP_NET_RAW.
>
> The policy is checked when timestamps are generated in the stack.
> It is possible for timestamps with data to be reported after the
> sysctl is set, if these were queued internally earlier.
>
> No vulnerability is immediately known that exploits knowledge
> gleaned from packet headers, but it may still be preferable to allow
> administrators to lock down this path at the cost of possible
> breakage of legacy applications.
>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>
> ----
>
> Changes (rfc -> v1)
> - document the sysctl in Documentation/sysctl/net.txt
> - fix access control race: read .._OPT_TSONLY only once,
> use same value for permission check and skb generation.
> ---
> Documentation/sysctl/net.txt | 8 ++++++++
> include/net/sock.h | 1 +
> net/core/skbuff.c | 10 +++++++++-
> net/core/sock.c | 3 +++
> net/core/sysctl_net_core.c | 9 +++++++++
> 5 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
> index 666594b..6294b51 100644
> --- a/Documentation/sysctl/net.txt
> +++ b/Documentation/sysctl/net.txt
> @@ -97,6 +97,14 @@ rmem_max
>
> The maximum receive socket buffer size in bytes.
>
> +tstamp_allow_data
> +-----------------
> +Allow processes to receive tx timestamps looped together with the original
> +packet contents. If disabled, transmit timestamp requests from unprivileged
> +processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
> +Default: 1 (on)
> +
> +
> wmem_default
> ------------
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 2210fec..9729171 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2262,6 +2262,7 @@ bool sk_net_capable(const struct sock *sk, int cap);
> extern __u32 sysctl_wmem_max;
> extern __u32 sysctl_rmem_max;
>
> +extern int sysctl_tstamp_allow_data;
> extern int sysctl_optmem_max;
>
> extern __u32 sysctl_wmem_default;
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 65a3798..333c62e 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3690,11 +3690,19 @@ static void __skb_complete_tx_timestamp(struct sk_buff *skb,
> kfree_skb(skb);
> }
>
> +static bool skb_may_tx_timestamp(struct sock *sk, bool tsonly)
> +{
> + return sysctl_tstamp_allow_data || capable(CAP_NET_RAW) || tsonly;
Immediately after hitting send discovered an issue with this patch,
sorry. This test for CAP_NET_RAW is not correct in this context. Will
have to either drop the CAP_NET_RAW exception to policy enforcement or
find another way of testing for it.
> +}
> +
> void skb_complete_tx_timestamp(struct sk_buff *skb,
> struct skb_shared_hwtstamps *hwtstamps)
> {
> struct sock *sk = skb->sk;
>
> + if (!skb_may_tx_timestamp(sk, false))
> + return;
> +
> /* take a reference to prevent skb_orphan() from freeing the socket */
> sock_hold(sk);
>
> @@ -3712,7 +3720,7 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
> struct sk_buff *skb;
> bool tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
>
> - if (!sk)
> + if (!sk || !skb_may_tx_timestamp(sk, tsonly))
> return;
>
> if (tsonly)
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 1c7a33d..93c8b20 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -325,6 +325,8 @@ __u32 sysctl_rmem_default __read_mostly = SK_RMEM_MAX;
> int sysctl_optmem_max __read_mostly = sizeof(unsigned long)*(2*UIO_MAXIOV+512);
> EXPORT_SYMBOL(sysctl_optmem_max);
>
> +int sysctl_tstamp_allow_data __read_mostly = 1;
> +
> struct static_key memalloc_socks = STATIC_KEY_INIT_FALSE;
> EXPORT_SYMBOL_GPL(memalloc_socks);
>
> @@ -840,6 +842,7 @@ set_rcvbuf:
> ret = -EINVAL;
> break;
> }
> +
> if (val & SOF_TIMESTAMPING_OPT_ID &&
> !(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)) {
> if (sk->sk_protocol == IPPROTO_TCP) {
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index 31baba2..fde21d1 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -321,6 +321,15 @@ static struct ctl_table net_core_table[] = {
> .mode = 0644,
> .proc_handler = proc_dointvec
> },
> + {
> + .procname = "tstamp_allow_data",
> + .data = &sysctl_tstamp_allow_data,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = &zero,
> + .extra2 = &one
> + },
> #ifdef CONFIG_RPS
> {
> .procname = "rps_sock_flow_entries",
> --
> 2.2.0.rc0.207.ga3a616c
>
--
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