Re: [PATCH v5 3/6] connector/cn_proc: Add filtering to fix some bugs

From: Liam R. Howlett
Date: Thu Jun 01 2023 - 14:05:45 EST

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* Anjali Kulkarni <anjali.k.kulkarni@xxxxxxxxxx> [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@xxxxxxxxxx>

Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>

> ---
> drivers/connector/cn_proc.c | 53 ++++++++++++++++++++++++++++-------
> 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, 96 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index ccac1c453080..84f38d2bd4b9 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 = 0, initial = 0;
> + struct sock *sk = NULL;
>
> /*
> * Events are reported with respect to the initial pid
> @@ -367,13 +381,32 @@ 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);
> + 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 */
> --
> 2.40.0
>

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