[PATCH 1/3] tracing/user_events: Ensure write index cannot be negative

Beau Belgrave
2023-04-11T21:17:19Z

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.

Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace")
Reported-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
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 cc8c6d8b69b5..e7dff24aa724 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -1821,6 +1821,9 @@ 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) {
--
2.25.1