Patch "tracing: Fix crash when it fails to alloc ring buffer" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

tracing: Fix crash when it fails to alloc ring buffer

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tracing-fix-crash-when-it-fails-to-alloc-ring-buffer.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jing Xia <[email protected]>
Date: Tue, 26 Dec 2017 15:12:53 +0800
Subject: tracing: Fix crash when it fails to alloc ring buffer

From: Jing Xia <[email protected]>

commit 24f2aaf952ee0b59f31c3a18b8b36c9e3d3c2cf5 upstream.

Double free of the ring buffer happens when it fails to alloc new ring buffer instance for max_buffer if TRACER_MAX_TRACE is configured. The root cause is that the pointer is not set to NULL after the buffer is freed in allocate_trace_buffers(), and the freeing of the ring buffer is invoked again later if the pointer is not equal to Null, as:

instance_mkdir()

    |-allocate_trace_buffers()
        |-allocate_trace_buffer(tr, &tr->trace_buffer...)
	|-allocate_trace_buffer(tr, &tr->max_buffer...)

          // allocate fail(-ENOMEM),first free
          // and the buffer pointer is not set to null
        |-ring_buffer_free(tr->trace_buffer.buffer)

       // out_free_tr
    |-free_trace_buffers()
        |-free_trace_buffer(&tr->trace_buffer);

	      //if trace_buffer is not null, free again
	    |-ring_buffer_free(buf->buffer)
                |-rb_free_cpu_buffer(buffer->buffers[cpu])
                    // ring_buffer_per_cpu is null, and
                    // crash in ring_buffer_per_cpu->pages

---
 kernel/trace/trace.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -6555,7 +6555,9 @@ static int allocate_trace_buffers(struct
 				    allocate_snapshot ? size : 1);
 	if (WARN_ON(ret)) {
 		ring_buffer_free(tr->trace_buffer.buffer);
+		tr->trace_buffer.buffer = NULL;
 		free_percpu(tr->trace_buffer.data);
+		tr->trace_buffer.data = NULL;
 		return -ENOMEM;
 	}
 	tr->allocated_snapshot = allocate_snapshot;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/tracing-fix-crash-when-it-fails-to-alloc-ring-buffer.patch queue-4.4/tracing-fix-possible-double-free-on-failure-of-allocating-trace-buffer.patch