[PATCH v2 01/18] tracing/remotes: Gate tracefs files opening on trace remote registration

[Vincent Donnefort <vdonnefort@google.com>]

Currently, if a remote fails to register, its resources will leak and
will not be properly tear-downed.

To prevent a user accessing a remote tracefs that is about to be
destroyed, keep track of the registered remotes in a global list,
similarly to trace instances. Gate the tracefs to open function based on
the presence of the remote in that list.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index d6c3f94d67cd..9f1669d433d5 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -39,6 +39,7 @@ struct trace_remote_iterator {
 };
 
 struct trace_remote {
+	struct list_head		node;
 	struct trace_remote_callbacks	*cbs;
 	void				*priv;
 	struct trace_buffer		*trace_buffer;
@@ -57,6 +58,9 @@ struct trace_remote {
 	bool				tracing_on;
 };
 
+static DEFINE_MUTEX(trace_remotes_lock);
+static LIST_HEAD(trace_remotes);
+
 static bool trace_remote_loaded(struct trace_remote *remote)
 {
 	return !!remote->trace_buffer;
@@ -170,6 +174,60 @@ static void trace_remote_reset(struct trace_remote *remote, int cpu)
 	trace_remote_try_unload(remote);
 }
 
+static int trace_remote_tracefs_open(struct inode *inode, struct file *filp)
+{
+	void *i_private = inode->i_private;
+	struct trace_remote *r;
+
+	if (!i_private)
+		return -ENODEV;
+
+	guard(mutex)(&trace_remotes_lock);
+
+	/* i_private is either a struct trace_remote or a struct remote_event */
+	list_for_each_entry(r, &trace_remotes, node) {
+		if (r == i_private)
+			return 0;
+		if (!r->events)
+			continue;
+		if (i_private >= (void *)r->events &&
+		    i_private < (void *)(r->events + r->nr_events))
+			return 0;
+	}
+
+	return -ENODEV;
+}
+
+#define DEFINE_TRACE_REMOTE_ATTRIBUTE_FUNCS(__name)			\
+static int __name ## _open(struct inode *inode, struct file *file)	\
+{									\
+	int ret = trace_remote_tracefs_open(inode, file);		\
+									\
+	if (ret)							\
+		return ret;						\
+									\
+	return single_open(file, __name ## _show, inode->i_private);	\
+}
+
+#define DEFINE_TRACE_REMOTE_ATTRIBUTE(__name)				\
+DEFINE_TRACE_REMOTE_ATTRIBUTE_FUNCS(__name)				\
+static const struct file_operations __name ## _fops = {			\
+	.open		= __name ## _open,				\
+	.read		= seq_read,					\
+	.write		= __name ## _write,				\
+	.llseek		= seq_lseek,					\
+	.release	= single_release,				\
+}
+
+#define DEFINE_TRACE_REMOTE_SHOW_ATTRIBUTE(__name)			\
+DEFINE_TRACE_REMOTE_ATTRIBUTE_FUNCS(__name)				\
+static const struct file_operations __name ## _fops = {			\
+	.open		= __name ## _open,				\
+	.read		= seq_read,					\
+	.llseek		= seq_lseek,					\
+	.release	= single_release,				\
+}
+
 static ssize_t
 tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
 {
@@ -198,7 +256,7 @@ static int tracing_on_show(struct seq_file *s, void *unused)
 
 	return 0;
 }
-DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on);
+DEFINE_TRACE_REMOTE_ATTRIBUTE(tracing_on);
 
 static ssize_t buffer_size_kb_write(struct file *filp, const char __user *ubuf, size_t cnt,
 				    loff_t *ppos)
@@ -235,7 +293,7 @@ static int buffer_size_kb_show(struct seq_file *s, void *unused)
 
 	return 0;
 }
-DEFINE_SHOW_STORE_ATTRIBUTE(buffer_size_kb);
+DEFINE_TRACE_REMOTE_ATTRIBUTE(buffer_size_kb);
 
 static int trace_remote_get(struct trace_remote *remote, int cpu)
 {
@@ -593,6 +651,11 @@ static int trace_pipe_open(struct inode *inode, struct file *filp)
 	struct trace_remote *remote = inode->i_private;
 	struct trace_remote_iterator *iter;
 	int cpu = tracing_get_cpu(inode);
+	int ret;
+
+	ret = trace_remote_tracefs_open(inode, filp);
+	if (ret)
+		return ret;
 
 	guard(mutex)(&remote->lock);
 
@@ -602,7 +665,7 @@ static int trace_pipe_open(struct inode *inode, struct file *filp)
 
 	filp->private_data = iter;
 
-	return IS_ERR(iter) ? PTR_ERR(iter) : 0;
+	return 0;
 }
 
 static int trace_pipe_release(struct inode *inode, struct file *filp)
@@ -734,22 +797,26 @@ static int trace_open(struct inode *inode, struct file *filp)
 	int cpu = tracing_get_cpu(inode);
 	int ret;
 
+	ret = trace_remote_tracefs_open(inode, filp);
+	if (ret)
+		return ret;
+
 	if (!(filp->f_mode & FMODE_READ))
 		return 0;
 
+	ret = seq_open(filp, &trace_sops);
+	if (ret)
+		return ret;
+
 	guard(mutex)(&remote->lock);
 
 	iter = trace_remote_iter(remote, cpu, TRI_NONCONSUMING);
-	if (IS_ERR(iter))
+	if (IS_ERR(iter)) {
+		seq_release(inode, filp);
 		return PTR_ERR(iter);
-
-	ret = seq_open(filp, &trace_sops);
-	if (ret) {
-		trace_remote_iter_free(iter);
-		return ret;
 	}
 
-	((struct seq_file *)filp->private_data)->private = (void *)iter;
+	((struct seq_file *)filp->private_data)->private = iter;
 
 	return 0;
 }
@@ -932,8 +999,12 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
 	}
 
 	ret = cbs->init ? cbs->init(remote->dentry, priv) : 0;
-	if (ret)
+	if (ret) {
 		pr_err("Init failed for trace remote '%s' (%d)\n", name, ret);
+	} else {
+		guard(mutex)(&trace_remotes_lock);
+		list_add(&remote->node, &trace_remotes);
+	}
 
 	return ret;
 }
@@ -1076,7 +1147,7 @@ static ssize_t remote_event_enable_write(struct file *filp, const char __user *u
 
 	return count;
 }
-DEFINE_SHOW_STORE_ATTRIBUTE(remote_event_enable);
+DEFINE_TRACE_REMOTE_ATTRIBUTE(remote_event_enable);
 
 static int remote_event_id_show(struct seq_file *s, void *unused)
 {
@@ -1086,7 +1157,7 @@ static int remote_event_id_show(struct seq_file *s, void *unused)
 
 	return 0;
 }
-DEFINE_SHOW_ATTRIBUTE(remote_event_id);
+DEFINE_TRACE_REMOTE_SHOW_ATTRIBUTE(remote_event_id);
 
 static int remote_event_format_show(struct seq_file *s, void *unused)
 {
@@ -1115,7 +1186,7 @@ static int remote_event_format_show(struct seq_file *s, void *unused)
 
 	return 0;
 }
-DEFINE_SHOW_ATTRIBUTE(remote_event_format);
+DEFINE_TRACE_REMOTE_SHOW_ATTRIBUTE(remote_event_format);
 
 static int remote_event_callback(const char *name, umode_t *mode, void **data,
 				 const struct file_operations **fops)
@@ -1190,6 +1261,7 @@ static ssize_t remote_events_dir_enable_read(struct file *filp, char __user *ubu
 }
 
 static const struct file_operations remote_events_dir_enable_fops = {
+	.open = trace_remote_tracefs_open,
 	.write = remote_events_dir_enable_write,
 	.read = remote_events_dir_enable_read,
 };
@@ -1214,6 +1286,7 @@ remote_events_dir_header_page_read(struct file *filp, char __user *ubuf, size_t
 }
 
 static const struct file_operations remote_events_dir_header_page_fops = {
+	.open = trace_remote_tracefs_open,
 	.read = remote_events_dir_header_page_read,
 };
 
@@ -1237,6 +1310,7 @@ remote_events_dir_header_event_read(struct file *filp, char __user *ubuf, size_t
 }
 
 static const struct file_operations remote_events_dir_header_event_fops = {
+	.open = trace_remote_tracefs_open,
 	.read = remote_events_dir_header_event_read,
 };
 
-- 
2.54.0.1032.g2f8565e1d1-goog