[PATCH 5.15.y] ftrace: Add global mutex to serialize trace_parser access

From: Tengda Wu <[email protected]>

[ Upstream commit 7720b63bcef3f54c7fe288774b720a227d54a306 ]

In ftrace, the trace_parser structure is allocated and initialized when
a trace file is opened, and is subsequently used across write and release
handlers to parse user input.

The affected handler paths and their specific functions are:
  - Open paths: ftrace_regex_open(), ftrace_graph_open()
  - Write paths: ftrace_regex_write(), ftrace_graph_write()
  - Release paths: ftrace_regex_release(), ftrace_graph_release()

If userspace opens a trace file descriptor and shares it across multiple
threads, concurrent write calls will race on the parser's internal state,
specifically the 'idx', 'cont', and 'buffer' fields, leading to corrupted
input or undefined behavior.

Fix this by adding a global mutex, parser_lock, to serialize all access
to trace_parser across write and release paths, preventing concurrent
corruption of parser state.

Fixes: e704eff3ff51 ("ftrace: Have set_graph_function handle multiple functions in one write")
Fixes: 689fd8b65d66 ("tracing: trace parser support for function and graph")
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Tengda Wu <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
[ Replaced `guard(mutex)(&parser_lock)` with explicit `mutex_lock`/`mutex_unlock` pairs because 5.15 builds `-std=gnu89` with `-Werror=declaration-after-statement`. ]
Signed-off-by: Sasha Levin <[email protected]>
---
 kernel/trace/ftrace.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index e86064b14259a..19d6782a93d29 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1042,6 +1042,12 @@ struct ftrace_ops global_ops = {
 					  FTRACE_OPS_FL_PID,
 };
 
+/*
+ * parser_lock - Protects trace_parser state against concurrent operations.
+ * Held across trace_get_user() and subsequent buffer parsing to prevent races.
+ */
+static DEFINE_MUTEX(parser_lock);
+
 /*
  * Used by the stack unwinder to know about dynamic ftrace trampolines.
  */
@@ -4928,6 +4934,8 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	/* iter->hash is a local copy, so we don't need regex_lock */
 
 	parser = &iter->parser;
+
+	mutex_lock(&parser_lock);
 	read = trace_get_user(parser, ubuf, cnt, ppos);
 
 	if (read >= 0 && trace_parser_loaded(parser) &&
@@ -4941,6 +4949,7 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 
 	ret = read;
  out:
+	mutex_unlock(&parser_lock);
 	return ret;
 }
 
@@ -5675,12 +5684,14 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
 		iter = file->private_data;
 
 	parser = &iter->parser;
+	mutex_lock(&parser_lock);
 	if (trace_parser_loaded(parser)) {
 		int enable = !(iter->flags & FTRACE_ITER_NOTRACE);
 
 		ftrace_process_regex(iter, parser->buffer,
 				     parser->idx, enable);
 	}
+	mutex_unlock(&parser_lock);
 
 	trace_parser_put(parser);
 
@@ -5998,10 +6009,12 @@ ftrace_graph_release(struct inode *inode, struct file *file)
 
 		parser = &fgd->parser;
 
+		mutex_lock(&parser_lock);
 		if (trace_parser_loaded((parser))) {
 			ret = ftrace_graph_set_hash(fgd->new_hash,
 						    parser->buffer);
 		}
+		mutex_unlock(&parser_lock);
 
 		trace_parser_put(parser);
 
@@ -6121,6 +6134,7 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
 
 	parser = &fgd->parser;
 
+	mutex_lock(&parser_lock);
 	read = trace_get_user(parser, ubuf, cnt, ppos);
 
 	if (read >= 0 && trace_parser_loaded(parser) &&
@@ -6134,6 +6148,7 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
 	if (!ret)
 		ret = read;
 
+	mutex_unlock(&parser_lock);
 	return ret;
 }
 
-- 
2.53.0