tracing: Add NULL checks for buffer in ring_buffer_free_read_page()

In a previous commit 7433632c9ff6, buffer, buffer->buffers and
buffer->buffers[cpu] in ring_buffer_wake_waiters() can be NULL,
and thus the related checks are added.

However, in the same call stack, these variables are also used in
ring_buffer_free_read_page():

tracing_buffers_release()
  ring_buffer_wake_waiters(iter->array_buffer->buffer)
    cpu_buffer = buffer->buffers[cpu] -> Add checks by previous commit
  ring_buffer_free_read_page(iter->array_buffer->buffer)
    cpu_buffer = buffer->buffers[cpu] -> No check

Thus, to avod possible null-pointer derefernces, the related checks
should be added.

These results are reported by a static tool designed by myself.

Link: https://lkml.kernel.org/r/20230113125501.760324-1-baijiaju1990@gmail.com
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index c366a0a9ddba4724da3db47cb270b3d149e8395b..45d4a23d604442db6e037a7d48300beec043866f 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5626,11 +5626,16 @@ EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
  */
 void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu, void *data)
 {
-       struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+       struct ring_buffer_per_cpu *cpu_buffer;
        struct buffer_data_page *bpage = data;
        struct page *page = virt_to_page(bpage);
        unsigned long flags;
 
+       if (!buffer || !buffer->buffers || !buffer->buffers[cpu])
+               return;
+
+       cpu_buffer = buffer->buffers[cpu];
+
        /* If the page is still in use someplace else, we can't reuse it */
        if (page_ref_count(page) > 1)
                goto out;