Re: [PATCH v4 1/1] binder: report txn errors via generic netlink (genl)

[Simon Horman <horms@kernel.org>]

On Mon, Oct 21, 2024 at 12:12:33PM -0700, Li Li wrote:
> From: Li Li <dualli@google.com>
> 
> Frozen tasks can't process binder transactions, so sync binder
> transactions will fail with BR_FROZEN_REPLY and async binder
> transactions will be queued in the kernel async binder buffer.
> As these queued async transactions accumulates over time, the async
> buffer will eventually be running out, denying all new transactions
> after that with BR_FAILED_REPLY.
> 
> In addition to the above cases, different kinds of binder error codes
> might be returned to the sender. However, the core Linux, or Android,
> system administration process never knows what's actually happening.
> 
> This patch introduces the Linux generic netlink messages into the binder
> driver so that the Linux/Android system administration process can
> listen to important events and take corresponding actions, like stopping
> a broken app from attacking the OS by sending huge amount of spamming
> binder transactions.
> 
> The new binder genl sources and headers are automatically generated from
> the corresponding binder_genl YAML spec. Don't modify them directly.
> 
> Signed-off-by: Li Li <dualli@google.com>

...

> diff --git a/drivers/android/binder.c b/drivers/android/binder.c

...

> @@ -2984,6 +2985,130 @@ static void binder_set_txn_from_error(struct binder_transaction *t, int id,
>  	binder_thread_dec_tmpref(from);
>  }
>  
> +/**
> + * binder_find_proc() - set binder report flags
> + * @pid:	the target process
> + */
> +static struct binder_proc *binder_find_proc(int pid)
> +{
> +	struct binder_proc *proc;
> +
> +	mutex_lock(&binder_procs_lock);
> +	hlist_for_each_entry(proc, &binder_procs, proc_node) {
> +		if (proc->pid == pid) {
> +			mutex_unlock(&binder_procs_lock);
> +			return proc;
> +		}
> +	}
> +	mutex_unlock(&binder_procs_lock);
> +
> +	return NULL;
> +}
> +
> +/**
> + * binder_genl_set_report() - set binder report flags
> + * @proc:	the binder_proc calling the ioctl

nit: binder_genl_set_report does not have a proc parameter,
     but it does have a context parameter.

> + * @pid:	the target process
> + * @flags:	the flags to set
> + *
> + * If pid is 0, the flags are applied to the whole binder context.
> + * Otherwise, the flags are applied to the specific process only.
> + */
> +static int binder_genl_set_report(struct binder_context *context, u32 pid, u32 flags)

...

>  static int __init init_binder_device(const char *name)
>  {
>  	int ret;
> @@ -6920,6 +7196,11 @@ static int __init init_binder_device(const char *name)

The code above this hunk looks like this:


	ret = misc_register(&binder_device->miscdev);
	if (ret < 0) {
		kfree(binder_device);
		return ret;
	}

>  
>  	hlist_add_head(&binder_device->hlist, &binder_devices);
>  
> +	binder_device->context.report_seq = (atomic_t)ATOMIC_INIT(0);
> +	ret = binder_genl_init(&binder_device->context.genl_family, name);
> +	if (ret < 0)
> +		kfree(binder_device);

So I think that binder_device->miscdev needs to be misc_deregister'ed
if we hit this error condition.

> +
>  	return ret;

Probably adding an unwind ladder like this makes sense (completely untested!):

	ret = misc_register(&binder_device->miscdev);
	if (ret < 0)
		goto err_misc_deregister;

	hlist_add_head(&binder_device->hlist, &binder_devices);

	binder_device->context.report_seq = (atomic_t)ATOMIC_INIT(0);
	ret = binder_genl_init(&binder_device->context.genl_family, name);
	if (ret < 0);
		goto err_misc_deregister;

	return 0;

err_misc_deregister:
	misc_deregister(&binder_device->miscdev);
err_free_dev:
	kfree(binder_device);
	return ret;

...

> diff --git a/drivers/android/binder_genl.h b/drivers/android/binder_genl.h

Perhaps it is because of a different version of net-next,
but with this patch applied on top of the current head commit
13feb6074a9f ("binder: report txn errors via generic netlink (genl)")
I see:

$ ./tools/net/ynl/ynl-regen.sh -f
$ git diff

diff --git a/include/uapi/linux/android/binder_genl.h b/include/uapi/linux/android/binder_genl.h
index ef5289133be5..93e58b370420 100644
--- a/include/uapi/linux/android/binder_genl.h
+++ b/include/uapi/linux/android/binder_genl.h
@@ -3,12 +3,17 @@
 /*	Documentation/netlink/specs/binder_genl.yaml */
 /* YNL-GEN uapi header */
 
-#ifndef _UAPI_LINUX_BINDER_GENL_H
-#define _UAPI_LINUX_BINDER_GENL_H
+#ifndef _UAPI_LINUX_ANDROID/BINDER_GENL_H
+#define _UAPI_LINUX_ANDROID/BINDER_GENL_H
 
 #define BINDER_GENL_FAMILY_NAME		"binder_genl"
 #define BINDER_GENL_FAMILY_VERSION	1
 
+/**
+ * enum binder_genl_flag - Used with "set" and "reply" command below, defining
+ *   what kind \ of binder transactions should be reported to the user space \
+ *   administration process.
+ */
 enum binder_genl_flag {
 	BINDER_GENL_FLAG_FAILED = 1,
 	BINDER_GENL_FLAG_DELAYED = 2,
@@ -34,4 +39,4 @@ enum {
 	BINDER_GENL_CMD_MAX = (__BINDER_GENL_CMD_MAX - 1)
 };
 
-#endif /* _UAPI_LINUX_BINDER_GENL_H */
+#endif /* _UAPI_LINUX_ANDROID/BINDER_GENL_H */

...

-- 
pw-bot: changes-requested