linux-kernel - Re: [PATCH V2] ring-buffer: fix overflow in __rb_map

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Message-ID: <20241218081800.05d81fe4@gandalf.local.home>
Date: Wed, 18 Dec 2024 08:18:00 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Edward Adam Davis <eadavis@...com>
Cc: vdonnefort@...gle.com, aha310510@...il.com, david@...hat.com,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 mathieu.desnoyers@...icios.com, mhiramat@...nel.org,
 syzbot+345e4443a21200874b18@...kaller.appspotmail.com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH V2] ring-buffer: fix overflow in __rb_map_vma

On Wed, 18 Dec 2024 19:42:22 +0800
Edward Adam Davis <eadavis@...com> wrote:

> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 7e257e855dd1..20f0e01b7a50 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -7019,7 +7019,11 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
>  	lockdep_assert_held(&cpu_buffer->mapping_lock);
>  
>  	nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
> -	nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff; /* + meta-page */
> +	nr_pages = ((nr_subbufs + 1) << subbuf_order); /* + meta-page */
> +	if (nr_pages < pgoff)

That probably should be <= as if it was equal...

> +		return -EINVAL;
> +
> +	nr_pages -= pgoff;

nr_pages would be zero and

>  
>  	nr_vma_pages = vma_pages(vma);
>  	if (!nr_vma_pages || nr_vma_pages > nr_pages)

this would return true, which the next line is:

		return -EINVAL;

Why not catch it before going through all that?

-- Steve


> --