Re: [PATCH] ring-buffer: Fix subbuf_ids memory leak in rb_allocate_cpu_buffer() error path

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Thu, 30 Jul 2026 09:13:08 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> On Thu, Jul 30, 2026 at 04:01:51PM +0900, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > In rb_allocate_cpu_buffer(), cpu_buffer->subbuf_ids is allocated using
> > kcalloc() when buffer->remote is non-NULL. If a subsequent page allocation
> > fails (e.g., ring_buffer_desc_page() returns NULL or rb_allocate_pages()
> > fails), execution jumps to fail_free_reader.
> > 
> > While __free(kfree) automatically frees the outer cpu_buffer structure
> > at scope exit, kfree(cpu_buffer) does not recursively free nested heap
> > pointers such as cpu_buffer->subbuf_ids, resulting in a memory leak.
> > 
> > Fix this by explicitly freeing cpu_buffer->subbuf_ids in the
> > fail_free_reader error unwinding path when cpu_buffer->remote is set.
> > 
> > Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes")
> > Assisted-by: Antigravity:gemini-3.6-flash
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---
> >  kernel/trace/ring_buffer.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index 78d3875a47a5..03f6baf6a5f5 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -2599,6 +2599,8 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
> >  	return_ptr(cpu_buffer);
> >  
> >   fail_free_reader:
> > +	if (cpu_buffer->remote)
> > +		kfree(cpu_buffer->subbuf_ids);
> 
> alloc_cpu_buffer() being kzalloc, I suppose here we could just unconditionally
> call kfree(cpu_buffer->subbuf_ids) ?
> 

Ah, indeed. Thanks for the comment!

> >  	free_buffer_page(cpu_buffer->reader_page);
> >  
> >  	return NULL;
> > 
> 
> -- 
> Vincent


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>