linux-kernel - [for-next][PATCH 05/11] tracing/user_events: Ensure write index cannot be negative

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Message-ID: <20230426171750.028699848@goodmis.org>
Date:   Wed, 26 Apr 2023 13:17:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Doug Cook <dcook@...ux.microsoft.com>,
        Beau Belgrave <beaub@...ux.microsoft.com>
Subject: [for-next][PATCH 05/11] tracing/user_events: Ensure write index cannot be negative

From: Beau Belgrave <beaub@...ux.microsoft.com>

The write index indicates which event the data is for and accesses a
per-file array. The index is passed by user processes during write()
calls as the first 4 bytes. Ensure that it cannot be negative by
returning -EINVAL to prevent out of bounds accesses.

Update ftrace self-test to ensure this occurs properly.

Link: https://lkml.kernel.org/r/20230425225107.8525-2-beaub@linux.microsoft.com

Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace")
Reported-by: Doug Cook <dcook@...ux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_user.c                  | 3 +++
 tools/testing/selftests/user_events/ftrace_test.c | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index eadb58a3efba..546d47a57520 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -1824,6 +1824,9 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
 	if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx)))
 		return -EFAULT;
 
+	if (idx < 0)
+		return -EINVAL;
+
 	rcu_read_lock_sched();
 
 	refs = rcu_dereference_sched(info->refs);
diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
index aceafacfb126..91272f9d6fce 100644
--- a/tools/testing/selftests/user_events/ftrace_test.c
+++ b/tools/testing/selftests/user_events/ftrace_test.c
@@ -296,6 +296,11 @@ TEST_F(user, write_events) {
 	ASSERT_NE(-1, writev(self->data_fd, (const struct iovec *)io, 3));
 	after = trace_bytes();
 	ASSERT_GT(after, before);
+
+	/* Negative index should fail with EINVAL */
+	reg.write_index = -1;
+	ASSERT_EQ(-1, writev(self->data_fd, (const struct iovec *)io, 3));
+	ASSERT_EQ(EINVAL, errno);
 }
 
 TEST_F(user, write_fault) {
-- 
2.39.2