ring_buffer_subbuf_order_set() stores the new order and only then walks the CPUs, returning -EBUSY if any of them has resizing disabled. A user mapped buffer has resizing disabled, and __rb_map_vma() reads buffer->subbuf_order without buffer->mutex, so an mmap of an already mapped CPU racing the failing order change sizes the mapping with the new order and inserts pages past the sub-buffer into the VMA. Check the CPUs before storing the new order. Fixes: 117c39200d9d ("ring-buffer: Introducing ring-buffer mapping functions") Cc: stable@vger.kernel.org Signed-off-by: David Carlier --- kernel/trace/ring_buffer.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..d7e5e4620d09 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7474,6 +7474,14 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) old_capacity = rb_subbuf_capacity(buffer); + /* The mmap fast path reads subbuf_order without buffer->mutex. */ + for_each_buffer_cpu(buffer, cpu) { + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + continue; + if (atomic_read(&buffer->buffers[cpu]->resize_disabled)) + return -EBUSY; + } + atomic_inc(&buffer->record_disabled); /* Make sure all commits have finished */ -- 2.55.0