[PATCH 0/1] tracing/user_events: Initial support for grouping

[PATCH 0/1] tracing/user_events: Initial support for grouping

[Beau Belgrave]

In order to enable namespaces, or any sort of isolation, within
user_events the register lock and pages need to be broken up into
groups. Each event and file now has a group pointer which stores
the actual pages to map, lookup data and synchronization objects.

There's been some previous discussion about this both in the
tracefs meetings as well as on the mailing lists:
Link: https://lore.kernel.org/all/20220312010140.1880-1-beaub@linux.microsoft.com/
Link: https://lore.kernel.org/all/20220425184631.2068-1-beaub@linux.microsoft.com/

This was also brought up in the most recent plumbers conference,
with some feedback to follow the IMA namespace model. This only enables
a single group that maps to init_user_ns, as IMA namespace has done.

Link: https://youtu.be/zai3gvpuEHc?t=4403
Link: https://lore.kernel.org/linux-kernel/20220915193221.1728029-15-stefanb@linux.ibm.com/#t

While it's not clear what all needs to be within a tracing namespace,
we have to start somewhere. The patch leaves out how new namespaces
are created and further configured by an operator. However, it
offers a structure and the minimum scaffolding to enable isolation
while we discuss this in further detail and build upon this in steps.

Beau Belgrave (1):
  tracing/user_events: Move pages/locks into groups to prepare for
    namespaces

 kernel/trace/trace_events_user.c | 346 ++++++++++++++++++++++++-------
 1 file changed, 274 insertions(+), 72 deletions(-)


base-commit: c23cbf0d23145ffd0f99520a5c1d65abba628936
-- 
2.25.1

[PATCH 1/1] tracing/user_events: Move pages/locks into groups to prepare for namespaces

[Beau Belgrave]

In order to enable namespaces or any sort of isolation within
user_events the register lock and pages need to be broken up into
groups. Each event and file now has a group pointer which stores the
actual pages to map, lookup data and synchronization objects.

This only enables a single group that maps to init_user_ns, as IMA
namespace has done. This enables user_events to start the work of
supporting namespaces by walking the namespaces up to the init_user_ns.
Future patches will address other user namespaces and will align to the
approaches the IMA namespace uses.

Link: https://lore.kernel.org/linux-kernel/20220915193221.1728029-15-stefanb@linux.ibm.com/#t

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
 kernel/trace/trace_events_user.c | 346 ++++++++++++++++++++++++-------
 1 file changed, 274 insertions(+), 72 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 2c0a6ec75548..ae78c2d53c8a 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -74,11 +74,25 @@
 #define EVENT_STATUS_PERF BIT(1)
 #define EVENT_STATUS_OTHER BIT(7)
 
-static char *register_page_data;
+/*
+ * Stores the pages, tables, and locks for a group of events.
+ * Each logical grouping of events has its own group, with a
+ * matching page for status checks within user programs. This
+ * allows for isolation of events to user programs by various
+ * means.
+ */
+struct user_event_group {
+	struct page *pages;
+	char *register_page_data;
+	char *system_name;
+	struct hlist_node node;
+	struct mutex reg_mutex;
+	DECLARE_HASHTABLE(register_table, 8);
+	DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
+};
 
-static DEFINE_MUTEX(reg_mutex);
-static DEFINE_HASHTABLE(register_table, 8);
-static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
+/* Group for init_user_ns mapping, top-most group */
+static struct user_event_group *init_group;
 
 /*
  * Stores per-event properties, as users register events
@@ -88,6 +102,7 @@ static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
  * refcnt reaches one.
  */
 struct user_event {
+	struct user_event_group *group;
 	struct tracepoint tracepoint;
 	struct trace_event_call call;
 	struct trace_event_class class;
@@ -114,6 +129,11 @@ struct user_event_refs {
 	struct user_event *events[];
 };
 
+struct user_event_file_info {
+	struct user_event_group *group;
+	struct user_event_refs *refs;
+};
+
 #define VALIDATOR_ENSURE_NULL (1 << 0)
 #define VALIDATOR_REL (1 << 1)
 
@@ -126,7 +146,8 @@ struct user_event_validator {
 typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
 				   void *tpdata, bool *faulted);
 
-static int user_event_parse(char *name, char *args, char *flags,
+static int user_event_parse(struct user_event_group *group, char *name,
+			    char *args, char *flags,
 			    struct user_event **newuser);
 
 static u32 user_event_key(char *name)
@@ -134,12 +155,128 @@ static u32 user_event_key(char *name)
 	return jhash(name, strlen(name), 0);
 }
 
+static void set_page_reservations(char *pages, bool set)
+{
+	int page;
+
+	for (page = 0; page < MAX_PAGES; ++page) {
+		void *addr = pages + (PAGE_SIZE * page);
+
+		if (set)
+			SetPageReserved(virt_to_page(addr));
+		else
+			ClearPageReserved(virt_to_page(addr));
+	}
+}
+
+static void user_event_group_destroy(struct user_event_group *group)
+{
+	if (group->register_page_data)
+		set_page_reservations(group->register_page_data, false);
+
+	if (group->pages)
+		__free_pages(group->pages, MAX_PAGE_ORDER);
+
+	kfree(group->system_name);
+	kfree(group);
+}
+
+static char *user_event_group_system_name(struct user_namespace *user_ns)
+{
+	char *system_name;
+	int len = sizeof(USER_EVENTS_SYSTEM) + 1;
+
+	if (user_ns != &init_user_ns) {
+		/*
+		 * Unexpected at this point:
+		 * We only currently support init_user_ns.
+		 * When we enable more, this will trigger a failure so log.
+		 */
+		pr_warn("user_events: Namespace other than init_user_ns!\n");
+		return NULL;
+	}
+
+	system_name = kmalloc(len, GFP_KERNEL);
+
+	if (!system_name)
+		return NULL;
+
+	snprintf(system_name, len, "%s", USER_EVENTS_SYSTEM);
+
+	return system_name;
+}
+
+static inline struct user_event_group
+*user_event_group_from_user_ns(struct user_namespace *user_ns)
+{
+	if (user_ns == &init_user_ns)
+		return init_group;
+
+	return NULL;
+}
+
+static struct user_event_group *current_user_event_group(void)
+{
+	struct user_namespace *user_ns = current_user_ns();
+	struct user_event_group *group = NULL;
+
+	while (user_ns) {
+		group = user_event_group_from_user_ns(user_ns);
+
+		if (group)
+			break;
+
+		user_ns = user_ns->parent;
+	}
+
+	return group;
+}
+
+static struct user_event_group
+*user_event_group_create(struct user_namespace *user_ns)
+{
+	struct user_event_group *group;
+
+	group = kzalloc(sizeof(*group), GFP_KERNEL);
+
+	if (!group)
+		return NULL;
+
+	group->system_name = user_event_group_system_name(user_ns);
+
+	if (!group->system_name)
+		goto error;
+
+	group->pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
+
+	if (!group->pages)
+		goto error;
+
+	group->register_page_data = page_address(group->pages);
+
+	set_page_reservations(group->register_page_data, true);
+
+	/* Zero all bits beside 0 (which is reserved for failures) */
+	bitmap_zero(group->page_bitmap, MAX_EVENTS);
+	set_bit(0, group->page_bitmap);
+
+	mutex_init(&group->reg_mutex);
+	hash_init(group->register_table);
+
+	return group;
+error:
+	if (group)
+		user_event_group_destroy(group);
+
+	return NULL;
+};
+
 static __always_inline
 void user_event_register_set(struct user_event *user)
 {
 	int i = user->index;
 
-	register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
+	user->group->register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
 }
 
 static __always_inline
@@ -147,7 +284,7 @@ void user_event_register_clear(struct user_event *user)
 {
 	int i = user->index;
 
-	register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
+	user->group->register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
 }
 
 static __always_inline __must_check
@@ -191,7 +328,8 @@ static struct list_head *user_event_get_fields(struct trace_event_call *call)
  *
  * Upon success user_event has its ref count increased by 1.
  */
-static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
+static int user_event_parse_cmd(struct user_event_group *group,
+				char *raw_command, struct user_event **newuser)
 {
 	char *name = raw_command;
 	char *args = strpbrk(name, " ");
@@ -205,7 +343,7 @@ static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
 	if (flags)
 		*flags++ = '\0';
 
-	return user_event_parse(name, args, flags, newuser);
+	return user_event_parse(group, name, args, flags, newuser);
 }
 
 static int user_field_array_size(const char *type)
@@ -693,7 +831,7 @@ static int destroy_user_event(struct user_event *user)
 	dyn_event_remove(&user->devent);
 
 	user_event_register_clear(user);
-	clear_bit(user->index, page_bitmap);
+	clear_bit(user->index, user->group->page_bitmap);
 	hash_del(&user->node);
 
 	user_event_destroy_validators(user);
@@ -704,14 +842,15 @@ static int destroy_user_event(struct user_event *user)
 	return ret;
 }
 
-static struct user_event *find_user_event(char *name, u32 *outkey)
+static struct user_event *find_user_event(struct user_event_group *group,
+					  char *name, u32 *outkey)
 {
 	struct user_event *user;
 	u32 key = user_event_key(name);
 
 	*outkey = key;
 
-	hash_for_each_possible(register_table, user, node, key)
+	hash_for_each_possible(group->register_table, user, node, key)
 		if (!strcmp(EVENT_NAME(user), name)) {
 			refcount_inc(&user->refcnt);
 			return user;
@@ -943,6 +1082,7 @@ static int user_event_reg(struct trace_event_call *call,
 
 static int user_event_create(const char *raw_command)
 {
+	struct user_event_group *group;
 	struct user_event *user;
 	char *name;
 	int ret;
@@ -958,14 +1098,19 @@ static int user_event_create(const char *raw_command)
 	if (!name)
 		return -ENOMEM;
 
-	mutex_lock(&reg_mutex);
+	group = current_user_event_group();
+
+	if (!group)
+		return -ENOENT;
+
+	mutex_lock(&group->reg_mutex);
 
-	ret = user_event_parse_cmd(name, &user);
+	ret = user_event_parse_cmd(group, name, &user);
 
 	if (!ret)
 		refcount_dec(&user->refcnt);
 
-	mutex_unlock(&reg_mutex);
+	mutex_unlock(&group->reg_mutex);
 
 	if (ret)
 		kfree(name);
@@ -1119,7 +1264,8 @@ static int user_event_trace_register(struct user_event *user)
  * The name buffer lifetime is owned by this method for success cases only.
  * Upon success the returned user_event has its ref count increased by 1.
  */
-static int user_event_parse(char *name, char *args, char *flags,
+static int user_event_parse(struct user_event_group *group, char *name,
+			    char *args, char *flags,
 			    struct user_event **newuser)
 {
 	int ret;
@@ -1129,7 +1275,7 @@ static int user_event_parse(char *name, char *args, char *flags,
 
 	/* Prevent dyn_event from racing */
 	mutex_lock(&event_mutex);
-	user = find_user_event(name, &key);
+	user = find_user_event(group, name, &key);
 	mutex_unlock(&event_mutex);
 
 	if (user) {
@@ -1142,7 +1288,7 @@ static int user_event_parse(char *name, char *args, char *flags,
 		return 0;
 	}
 
-	index = find_first_zero_bit(page_bitmap, MAX_EVENTS);
+	index = find_first_zero_bit(group->page_bitmap, MAX_EVENTS);
 
 	if (index == MAX_EVENTS)
 		return -EMFILE;
@@ -1156,6 +1302,7 @@ static int user_event_parse(char *name, char *args, char *flags,
 	INIT_LIST_HEAD(&user->fields);
 	INIT_LIST_HEAD(&user->validators);
 
+	user->group = group;
 	user->tracepoint.name = name;
 
 	ret = user_event_parse_fields(user, args);
@@ -1174,8 +1321,8 @@ static int user_event_parse(char *name, char *args, char *flags,
 	user->call.flags = TRACE_EVENT_FL_TRACEPOINT;
 	user->call.tp = &user->tracepoint;
 	user->call.event.funcs = &user_event_funcs;
+	user->class.system = group->system_name;
 
-	user->class.system = USER_EVENTS_SYSTEM;
 	user->class.fields_array = user_event_fields_array;
 	user->class.get_fields = user_event_get_fields;
 	user->class.reg = user_event_reg;
@@ -1198,8 +1345,8 @@ static int user_event_parse(char *name, char *args, char *flags,
 
 	dyn_event_init(&user->devent, &user_event_dops);
 	dyn_event_add(&user->devent, &user->call);
-	set_bit(user->index, page_bitmap);
-	hash_add(register_table, &user->node, key);
+	set_bit(user->index, group->page_bitmap);
+	hash_add(group->register_table, &user->node, key);
 
 	mutex_unlock(&event_mutex);
 
@@ -1217,10 +1364,10 @@ static int user_event_parse(char *name, char *args, char *flags,
 /*
  * Deletes a previously created event if it is no longer being used.
  */
-static int delete_user_event(char *name)
+static int delete_user_event(struct user_event_group *group, char *name)
 {
 	u32 key;
-	struct user_event *user = find_user_event(name, &key);
+	struct user_event *user = find_user_event(group, name, &key);
 
 	if (!user)
 		return -ENOENT;
@@ -1238,6 +1385,7 @@ static int delete_user_event(char *name)
  */
 static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
 {
+	struct user_event_file_info *info = file->private_data;
 	struct user_event_refs *refs;
 	struct user_event *user = NULL;
 	struct tracepoint *tp;
@@ -1249,7 +1397,7 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
 
 	rcu_read_lock_sched();
 
-	refs = rcu_dereference_sched(file->private_data);
+	refs = rcu_dereference_sched(info->refs);
 
 	/*
 	 * The refs->events array is protected by RCU, and new items may be
@@ -1307,6 +1455,28 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
 	return ret;
 }
 
+static int user_events_open(struct inode *node, struct file *file)
+{
+	struct user_event_group *group;
+	struct user_event_file_info *info;
+
+	group = current_user_event_group();
+
+	if (!group)
+		return -ENOENT;
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+
+	if (!info)
+		return -ENOMEM;
+
+	info->group = group;
+
+	file->private_data = info;
+
+	return 0;
+}
+
 static ssize_t user_events_write(struct file *file, const char __user *ubuf,
 				 size_t count, loff_t *ppos)
 {
@@ -1328,13 +1498,15 @@ static ssize_t user_events_write_iter(struct kiocb *kp, struct iov_iter *i)
 	return user_events_write_core(kp->ki_filp, i);
 }
 
-static int user_events_ref_add(struct file *file, struct user_event *user)
+static int user_events_ref_add(struct user_event_file_info *info,
+			       struct user_event *user)
 {
+	struct user_event_group *group = info->group;
 	struct user_event_refs *refs, *new_refs;
 	int i, size, count = 0;
 
-	refs = rcu_dereference_protected(file->private_data,
-					 lockdep_is_held(&reg_mutex));
+	refs = rcu_dereference_protected(info->refs,
+					 lockdep_is_held(&group->reg_mutex));
 
 	if (refs) {
 		count = refs->count;
@@ -1360,7 +1532,7 @@ static int user_events_ref_add(struct file *file, struct user_event *user)
 
 	refcount_inc(&user->refcnt);
 
-	rcu_assign_pointer(file->private_data, new_refs);
+	rcu_assign_pointer(info->refs, new_refs);
 
 	if (refs)
 		kfree_rcu(refs, rcu);
@@ -1397,7 +1569,8 @@ static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
 /*
  * Registers a user_event on behalf of a user process.
  */
-static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
+static long user_events_ioctl_reg(struct user_event_file_info *info,
+				  unsigned long uarg)
 {
 	struct user_reg __user *ureg = (struct user_reg __user *)uarg;
 	struct user_reg reg;
@@ -1418,14 +1591,14 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
 		return ret;
 	}
 
-	ret = user_event_parse_cmd(name, &user);
+	ret = user_event_parse_cmd(info->group, name, &user);
 
 	if (ret) {
 		kfree(name);
 		return ret;
 	}
 
-	ret = user_events_ref_add(file, user);
+	ret = user_events_ref_add(info, user);
 
 	/* No longer need parse ref, ref_add either worked or not */
 	refcount_dec(&user->refcnt);
@@ -1443,7 +1616,8 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
 /*
  * Deletes a user_event on behalf of a user process.
  */
-static long user_events_ioctl_del(struct file *file, unsigned long uarg)
+static long user_events_ioctl_del(struct user_event_file_info *info,
+				  unsigned long uarg)
 {
 	void __user *ubuf = (void __user *)uarg;
 	char *name;
@@ -1456,7 +1630,7 @@ static long user_events_ioctl_del(struct file *file, unsigned long uarg)
 
 	/* event_mutex prevents dyn_event from racing */
 	mutex_lock(&event_mutex);
-	ret = delete_user_event(name);
+	ret = delete_user_event(info->group, name);
 	mutex_unlock(&event_mutex);
 
 	kfree(name);
@@ -1470,19 +1644,21 @@ static long user_events_ioctl_del(struct file *file, unsigned long uarg)
 static long user_events_ioctl(struct file *file, unsigned int cmd,
 			      unsigned long uarg)
 {
+	struct user_event_file_info *info = file->private_data;
+	struct user_event_group *group = info->group;
 	long ret = -ENOTTY;
 
 	switch (cmd) {
 	case DIAG_IOCSREG:
-		mutex_lock(&reg_mutex);
-		ret = user_events_ioctl_reg(file, uarg);
-		mutex_unlock(&reg_mutex);
+		mutex_lock(&group->reg_mutex);
+		ret = user_events_ioctl_reg(info, uarg);
+		mutex_unlock(&group->reg_mutex);
 		break;
 
 	case DIAG_IOCSDEL:
-		mutex_lock(&reg_mutex);
-		ret = user_events_ioctl_del(file, uarg);
-		mutex_unlock(&reg_mutex);
+		mutex_lock(&group->reg_mutex);
+		ret = user_events_ioctl_del(info, uarg);
+		mutex_unlock(&group->reg_mutex);
 		break;
 	}
 
@@ -1494,17 +1670,24 @@ static long user_events_ioctl(struct file *file, unsigned int cmd,
  */
 static int user_events_release(struct inode *node, struct file *file)
 {
+	struct user_event_file_info *info = file->private_data;
+	struct user_event_group *group;
 	struct user_event_refs *refs;
 	struct user_event *user;
 	int i;
 
+	if (!info)
+		return -EINVAL;
+
+	group = info->group;
+
 	/*
 	 * Ensure refs cannot change under any situation by taking the
 	 * register mutex during the final freeing of the references.
 	 */
-	mutex_lock(&reg_mutex);
+	mutex_lock(&group->reg_mutex);
 
-	refs = file->private_data;
+	refs = info->refs;
 
 	if (!refs)
 		goto out;
@@ -1523,32 +1706,51 @@ static int user_events_release(struct inode *node, struct file *file)
 out:
 	file->private_data = NULL;
 
-	mutex_unlock(&reg_mutex);
+	mutex_unlock(&group->reg_mutex);
 
 	kfree(refs);
+	kfree(info);
 
 	return 0;
 }
 
 static const struct file_operations user_data_fops = {
+	.open = user_events_open,
 	.write = user_events_write,
 	.write_iter = user_events_write_iter,
 	.unlocked_ioctl	= user_events_ioctl,
 	.release = user_events_release,
 };
 
+static struct user_event_group *user_status_group(struct file *file)
+{
+	struct seq_file *m = file->private_data;
+
+	if (!m)
+		return NULL;
+
+	return m->private;
+}
+
 /*
  * Maps the shared page into the user process for checking if event is enabled.
  */
 static int user_status_mmap(struct file *file, struct vm_area_struct *vma)
 {
+	char *pages;
+	struct user_event_group *group = user_status_group(file);
 	unsigned long size = vma->vm_end - vma->vm_start;
 
 	if (size != MAX_BYTES)
 		return -EINVAL;
 
+	if (!group)
+		return -EINVAL;
+
+	pages = group->register_page_data;
+
 	return remap_pfn_range(vma, vma->vm_start,
-			       virt_to_phys(register_page_data) >> PAGE_SHIFT,
+			       virt_to_phys(pages) >> PAGE_SHIFT,
 			       size, vm_get_page_prot(VM_READ));
 }
 
@@ -1572,13 +1774,17 @@ static void user_seq_stop(struct seq_file *m, void *p)
 
 static int user_seq_show(struct seq_file *m, void *p)
 {
+	struct user_event_group *group = m->private;
 	struct user_event *user;
 	char status;
 	int i, active = 0, busy = 0, flags;
 
-	mutex_lock(&reg_mutex);
+	if (!group)
+		return -EINVAL;
+
+	mutex_lock(&group->reg_mutex);
 
-	hash_for_each(register_table, i, user, node) {
+	hash_for_each(group->register_table, i, user, node) {
 		status = user->status;
 		flags = user->flags;
 
@@ -1602,7 +1808,7 @@ static int user_seq_show(struct seq_file *m, void *p)
 		active++;
 	}
 
-	mutex_unlock(&reg_mutex);
+	mutex_unlock(&group->reg_mutex);
 
 	seq_puts(m, "\n");
 	seq_printf(m, "Active: %d\n", active);
@@ -1621,7 +1827,24 @@ static const struct seq_operations user_seq_ops = {
 
 static int user_status_open(struct inode *node, struct file *file)
 {
-	return seq_open(file, &user_seq_ops);
+	struct user_event_group *group;
+	int ret;
+
+	group = current_user_event_group();
+
+	if (!group)
+		return -ENOENT;
+
+	ret = seq_open(file, &user_seq_ops);
+
+	if (!ret) {
+		/* Chain group to seq_file */
+		struct seq_file *m = file->private_data;
+
+		m->private = group;
+	}
+
+	return ret;
 }
 
 static const struct file_operations user_status_fops = {
@@ -1662,42 +1885,21 @@ static int create_user_tracefs(void)
 	return -ENODEV;
 }
 
-static void set_page_reservations(bool set)
-{
-	int page;
-
-	for (page = 0; page < MAX_PAGES; ++page) {
-		void *addr = register_page_data + (PAGE_SIZE * page);
-
-		if (set)
-			SetPageReserved(virt_to_page(addr));
-		else
-			ClearPageReserved(virt_to_page(addr));
-	}
-}
-
 static int __init trace_events_user_init(void)
 {
-	struct page *pages;
 	int ret;
 
-	/* Zero all bits beside 0 (which is reserved for failures) */
-	bitmap_zero(page_bitmap, MAX_EVENTS);
-	set_bit(0, page_bitmap);
+	init_group = user_event_group_create(&init_user_ns);
 
-	pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
-	if (!pages)
+	if (!init_group)
 		return -ENOMEM;
-	register_page_data = page_address(pages);
-
-	set_page_reservations(true);
 
 	ret = create_user_tracefs();
 
 	if (ret) {
 		pr_warn("user_events could not register with tracefs\n");
-		set_page_reservations(false);
-		__free_pages(pages, MAX_PAGE_ORDER);
+		user_event_group_destroy(init_group);
+		init_group = NULL;
 		return ret;
 	}
 
-- 
2.25.1