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Date:   Fri, 7 Jul 2023 10:04:59 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Anjali Kulkarni <anjali.k.kulkarni@oracle.com>
Cc:     davem@davemloft.net, david@fries.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, zbr@ioremap.net,
        brauner@kernel.org, johannes@sipsolutions.net,
        ecree.xilinx@gmail.com, leon@kernel.org, keescook@chromium.org,
        socketcan@hartkopp.net, petrm@nvidia.com,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH v7 3/6] connector/cn_proc: Add filtering to fix some bugs
Message-ID: <20230707140459.qsyjw5i6chpbzqwj@revolver>
References: <20230704001136.2301645-1-anjali.k.kulkarni@oracle.com>
 <20230704001136.2301645-4-anjali.k.kulkarni@oracle.com>
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* Anjali Kulkarni <anjali.k.kulkarni@oracle.com> [691231 23:00]:
> The current proc connector code has the foll. bugs - if there are more
> than one listeners for the proc connector messages, and one of them
> deregisters for listening using PROC_CN_MCAST_IGNORE, they will still get
> all proc connector messages, as long as there is another listener.
> 
> Another issue is if one client calls PROC_CN_MCAST_LISTEN, and another one
> calls PROC_CN_MCAST_IGNORE, then both will end up not getting any messages.
> 
> This patch adds filtering and drops packet if client has sent
> PROC_CN_MCAST_IGNORE. This data is stored in the client socket's
> sk_user_data. In addition, we only increment or decrement
> proc_event_num_listeners once per client. This fixes the above issues.
> 
> cn_release is the release function added for NETLINK_CONNECTOR. It uses
> the newly added netlink_release function added to netlink_sock. It will
> free sk_user_data.
> 
> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@oracle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  drivers/connector/cn_proc.c   | 57 +++++++++++++++++++++++++++++------
>  drivers/connector/connector.c | 21 ++++++++++---
>  drivers/w1/w1_netlink.c       |  6 ++--
>  include/linux/connector.h     |  8 ++++-
>  include/uapi/linux/cn_proc.h  | 43 +++++++++++++++-----------
>  5 files changed, 100 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index ccac1c453080..1ba288ed2bf7 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -48,6 +48,21 @@ static DEFINE_PER_CPU(struct local_event, local_event) = {
>  	.lock = INIT_LOCAL_LOCK(lock),
>  };
>  
> +static int cn_filter(struct sock *dsk, struct sk_buff *skb, void *data)
> +{
> +	enum proc_cn_mcast_op mc_op;
> +
> +	if (!dsk)
> +		return 0;
> +
> +	mc_op = ((struct proc_input *)(dsk->sk_user_data))->mcast_op;
> +
> +	if (mc_op == PROC_CN_MCAST_IGNORE)
> +		return 1;
> +
> +	return 0;
> +}
> +
>  static inline void send_msg(struct cn_msg *msg)
>  {
>  	local_lock(&local_event.lock);
> @@ -61,7 +76,8 @@ static inline void send_msg(struct cn_msg *msg)
>  	 *
>  	 * If cn_netlink_send() fails, the data is not sent.
>  	 */
> -	cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT);
> +	cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> +			     cn_filter, NULL);
>  
>  	local_unlock(&local_event.lock);
>  }
> @@ -346,11 +362,9 @@ static void cn_proc_ack(int err, int rcvd_seq, int rcvd_ack)
>  static void cn_proc_mcast_ctl(struct cn_msg *msg,
>  			      struct netlink_skb_parms *nsp)
>  {
> -	enum proc_cn_mcast_op *mc_op = NULL;
> -	int err = 0;
> -
> -	if (msg->len != sizeof(*mc_op))
> -		return;
> +	enum proc_cn_mcast_op mc_op = 0, prev_mc_op = 0;
> +	int err = 1, initial = 0;
> +	struct sock *sk = NULL;
>  
>  	/* 
>  	 * Events are reported with respect to the initial pid
> @@ -367,13 +381,36 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
>  		goto out;
>  	}
>  
> -	mc_op = (enum proc_cn_mcast_op *)msg->data;
> -	switch (*mc_op) {
> +	if (msg->len == sizeof(mc_op))
> +		mc_op = *((enum proc_cn_mcast_op *)msg->data);
> +	else
> +		return;
> +
> +	if (nsp->sk) {
> +		sk = nsp->sk;
> +		if (sk->sk_user_data == NULL) {
> +			sk->sk_user_data = kzalloc(sizeof(struct proc_input),
> +						   GFP_KERNEL);
> +			if (sk->sk_user_data == NULL) {
> +				err = ENOMEM;
> +				goto out;
> +			}
> +			initial = 1;
> +		} else {
> +			prev_mc_op =
> +			((struct proc_input *)(sk->sk_user_data))->mcast_op;
> +		}
> +		((struct proc_input *)(sk->sk_user_data))->mcast_op = mc_op;
> +	}
> +
> +	switch (mc_op) {
>  	case PROC_CN_MCAST_LISTEN:
> -		atomic_inc(&proc_event_num_listeners);
> +		if (initial || (prev_mc_op != PROC_CN_MCAST_LISTEN))
> +			atomic_inc(&proc_event_num_listeners);
>  		break;
>  	case PROC_CN_MCAST_IGNORE:
> -		atomic_dec(&proc_event_num_listeners);
> +		if (!initial && (prev_mc_op != PROC_CN_MCAST_IGNORE))
> +			atomic_dec(&proc_event_num_listeners);
>  		break;
>  	default:
>  		err = EINVAL;
> diff --git a/drivers/connector/connector.c b/drivers/connector/connector.c
> index 48ec7ce6ecac..d1179df2b0ba 100644
> --- a/drivers/connector/connector.c
> +++ b/drivers/connector/connector.c
> @@ -59,7 +59,9 @@ static int cn_already_initialized;
>   * both, or if both are zero then the group is looked up and sent there.
>   */
>  int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 __group,
> -	gfp_t gfp_mask)
> +	gfp_t gfp_mask,
> +	int (*filter)(struct sock *dsk, struct sk_buff *skb, void *data),
> +	void *filter_data)
>  {
>  	struct cn_callback_entry *__cbq;
>  	unsigned int size;
> @@ -110,8 +112,9 @@ int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 __group,
>  	NETLINK_CB(skb).dst_group = group;
>  
>  	if (group)
> -		return netlink_broadcast(dev->nls, skb, portid, group,
> -					 gfp_mask);
> +		return netlink_broadcast_filtered(dev->nls, skb, portid, group,
> +						  gfp_mask, filter,
> +						  (void *)filter_data);
>  	return netlink_unicast(dev->nls, skb, portid,
>  			!gfpflags_allow_blocking(gfp_mask));
>  }
> @@ -121,7 +124,8 @@ EXPORT_SYMBOL_GPL(cn_netlink_send_mult);
>  int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group,
>  	gfp_t gfp_mask)
>  {
> -	return cn_netlink_send_mult(msg, msg->len, portid, __group, gfp_mask);
> +	return cn_netlink_send_mult(msg, msg->len, portid, __group, gfp_mask,
> +				    NULL, NULL);
>  }
>  EXPORT_SYMBOL_GPL(cn_netlink_send);
>  
> @@ -162,6 +166,14 @@ static int cn_call_callback(struct sk_buff *skb)
>  	return err;
>  }
>  
> +static void cn_release(struct sock *sk, unsigned long *groups)
> +{
> +	if (groups && test_bit(CN_IDX_PROC - 1, groups)) {
> +		kfree(sk->sk_user_data);
> +		sk->sk_user_data = NULL;
> +	}
> +}
> +
>  /*
>   * Main netlink receiving function.
>   *
> @@ -249,6 +261,7 @@ static int cn_init(void)
>  	struct netlink_kernel_cfg cfg = {
>  		.groups	= CN_NETLINK_USERS + 0xf,
>  		.input	= cn_rx_skb,
> +		.release = cn_release,
>  	};
>  
>  	dev->nls = netlink_kernel_create(&init_net, NETLINK_CONNECTOR, &cfg);
> diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
> index db110cc442b1..691978cddab7 100644
> --- a/drivers/w1/w1_netlink.c
> +++ b/drivers/w1/w1_netlink.c
> @@ -65,7 +65,8 @@ static void w1_unref_block(struct w1_cb_block *block)
>  		u16 len = w1_reply_len(block);
>  		if (len) {
>  			cn_netlink_send_mult(block->first_cn, len,
> -				block->portid, 0, GFP_KERNEL);
> +					     block->portid, 0,
> +					     GFP_KERNEL, NULL, NULL);
>  		}
>  		kfree(block);
>  	}
> @@ -83,7 +84,8 @@ static void w1_reply_make_space(struct w1_cb_block *block, u16 space)
>  {
>  	u16 len = w1_reply_len(block);
>  	if (len + space >= block->maxlen) {
> -		cn_netlink_send_mult(block->first_cn, len, block->portid, 0, GFP_KERNEL);
> +		cn_netlink_send_mult(block->first_cn, len, block->portid,
> +				     0, GFP_KERNEL, NULL, NULL);
>  		block->first_cn->len = 0;
>  		block->cn = NULL;
>  		block->msg = NULL;
> diff --git a/include/linux/connector.h b/include/linux/connector.h
> index 487350bb19c3..cec2d99ae902 100644
> --- a/include/linux/connector.h
> +++ b/include/linux/connector.h
> @@ -90,13 +90,19 @@ void cn_del_callback(const struct cb_id *id);
>   *		If @group is not zero, then message will be delivered
>   *		to the specified group.
>   * @gfp_mask:	GFP mask.
> + * @filter:     Filter function to be used at netlink layer.
> + * @filter_data:Filter data to be supplied to the filter function
>   *
>   * It can be safely called from softirq context, but may silently
>   * fail under strong memory pressure.
>   *
>   * If there are no listeners for given group %-ESRCH can be returned.
>   */
> -int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 group, gfp_t gfp_mask);
> +int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid,
> +			 u32 group, gfp_t gfp_mask,
> +			 int (*filter)(struct sock *dsk, struct sk_buff *skb,
> +				       void *data),
> +			 void *filter_data);
>  
>  /**
>   * cn_netlink_send - Sends message to the specified groups.
> diff --git a/include/uapi/linux/cn_proc.h b/include/uapi/linux/cn_proc.h
> index db210625cee8..6a06fb424313 100644
> --- a/include/uapi/linux/cn_proc.h
> +++ b/include/uapi/linux/cn_proc.h
> @@ -30,6 +30,30 @@ enum proc_cn_mcast_op {
>  	PROC_CN_MCAST_IGNORE = 2
>  };
>  
> +enum proc_cn_event {
> +	/* Use successive bits so the enums can be used to record
> +	 * sets of events as well
> +	 */
> +	PROC_EVENT_NONE = 0x00000000,
> +	PROC_EVENT_FORK = 0x00000001,
> +	PROC_EVENT_EXEC = 0x00000002,
> +	PROC_EVENT_UID  = 0x00000004,
> +	PROC_EVENT_GID  = 0x00000040,
> +	PROC_EVENT_SID  = 0x00000080,
> +	PROC_EVENT_PTRACE = 0x00000100,
> +	PROC_EVENT_COMM = 0x00000200,
> +	/* "next" should be 0x00000400 */
> +	/* "last" is the last process event: exit,
> +	 * while "next to last" is coredumping event
> +	 */
> +	PROC_EVENT_COREDUMP = 0x40000000,
> +	PROC_EVENT_EXIT = 0x80000000
> +};
> +
> +struct proc_input {
> +	enum proc_cn_mcast_op mcast_op;
> +};
> +
>  /*
>   * From the user's point of view, the process
>   * ID is the thread group ID and thread ID is the internal
> @@ -44,24 +68,7 @@ enum proc_cn_mcast_op {
>   */
>  
>  struct proc_event {
> -	enum what {
> -		/* Use successive bits so the enums can be used to record
> -		 * sets of events as well
> -		 */
> -		PROC_EVENT_NONE = 0x00000000,
> -		PROC_EVENT_FORK = 0x00000001,
> -		PROC_EVENT_EXEC = 0x00000002,
> -		PROC_EVENT_UID  = 0x00000004,
> -		PROC_EVENT_GID  = 0x00000040,
> -		PROC_EVENT_SID  = 0x00000080,
> -		PROC_EVENT_PTRACE = 0x00000100,
> -		PROC_EVENT_COMM = 0x00000200,
> -		/* "next" should be 0x00000400 */
> -		/* "last" is the last process event: exit,
> -		 * while "next to last" is coredumping event */
> -		PROC_EVENT_COREDUMP = 0x40000000,
> -		PROC_EVENT_EXIT = 0x80000000
> -	} what;
> +	enum proc_cn_event what;
>  	__u32 cpu;
>  	__u64 __attribute__((aligned(8))) timestamp_ns;
>  		/* Number of nano seconds since system boot */
> -- 
> 2.41.0
>